D&D 5E 5e Updates: Monstrous Compendium

[dave2008]

I have added a list of the Monsters by CR with a link in the OP.

 

[imeannoharm]

No. Demogorgon is the Prince of Demons, implying he is the strongest. However, he has no control or sovereignty over the other demon lords. Only the King of Demons has that power. Currently no demon holds the title of "King of Demons."

The king of demons sounds pretty bad-A. What’s the CR range?

 

[dave2008]

The king of demons sounds pretty bad-A. What’s the CR range?

Not sure, no plans to stat it at the moment. Probably in the CR35+ range with another mythic stage (similar to greater gods).

 

[dave2008]

Dungeons and Dragons Monster III Aboleth by gabrieldevue

Aboleth Lasher	Challenge 7
Large aberration, lawful evil	4,350 XP

Armor Class 17 (natural armor)
Hit Points 127 (17d10 + 34; bloodied 63)
Speed 10 ft., swim 40 ft.

STR	DEX	CON	INT	WIS	CHA
20 (+4)	18 (+4)	15 (+2)	18 (+4)	13 (+1)	17 (+3)

Savings Throws Dex +4, Con +5, Int +7, Wis +4
Skills Acrobatics +7, History +10, Perception +7, Stealth +7
Damage Resistances psychic
Senses darkvision 120 ft., passive Perception 17
Languages Deep Speech, telepathy 120 ft.
Proficiency Bonus +3; Maneuver DC 16

Amphibious. The aboleth can breathe air and water.

Aquatic. While underwater, the aboleth has advantage on melee attacks against creatures that do not have a swim speed. While out of water, the aboleth has disadvantage on Dexterity checks and saving throws.

Mucous Haze. The aboleth is surrounded by a cloud of mucus that extends for a 10-foot radius (20-foot radius in water) around the aboleth. The haze is difficult terrain, accept for aboleths, and creatures inside the haze are lightly obscured, except from aboleths.

Pack Tactics. The aboleth has advantage on an attack roll against a creature if it at least one of the aboleth’s allies is within 10 ft. of the creature and the ally isn’t incapacitated.

ACTIONS
Multiattack. The aboleth makes up to three melee attacks, but only one can be a bite or tail attack.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target grappled by the aboleth or incapacitated. Hit: 11 (2d6 + 4) piercing damage plus 3 (1d6) acid damage.

Tentacle. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage and the target must make a DC 15 Strength saving throw or be grappled.

Tail. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.

Enslave (1/Day). The aboleth targets one creature it can see within 60 feet of it. The target must succeed on a DC 14 Wisdom saving throw or be magically charmed by the aboleth until the aboleth dies or until it is on a different plane of existence from the target. The charmed target is under the aboleth’s control and can’t take reactions, and the aboleth and the target communicate telepathically with each other over any distance. The target has disadvantage on the saving throw if it is grappled by the aboleth.

Whenever the charmed target takes damage, the target can repeat the saving throw. On a success, the effect ends. No more than once every 24 hours, the target can also repeat the saving throw when it is at least one mile away from the aboleth.

BONUS ACTIONS
Quick Strikes. The aboleth can make two additional tentacle attacks on a target is has advantage against.

REACTIONS
Psychic Drain (Recharge 4-6). If a creature is charmed by the aboleth, on that creatures turn the aboleth can inflict 7 (2d6) psychic damage on the charmed creature, and the aboleth regains hit points equal to the damage the creature takes.

Vicious Bite. If a creature ends its turn grappled by the aboleth, the aboleth can make a bite attack against the grappled creature.

 

[dave2008]

Aboleth by MadMosquito

Aboleth Overseer	Challenge 9
Large elite aberration, lawful evil	10,000 elite XP

Armor Class 18 (natural armor)
Hit Points 187 (22d10 + 66; bloodied 93)
Speed 10 ft., swim 50 ft.

STR	DEX	CON	INT	WIS	CHA
22 (+6)	10 (+0)	16 (+3)	20 (+5)	15 (+2)	20 (+5)

Savings Throws Dex +4, Int +9, Wis +6
Skills History +14, Insight +6, Perception +10, Stealth +4
Damage Resistances acid, poison, psychic
Senses darkvision 120 ft., passive Perception 20
Languages Deep Speech, telepathy 180 ft.
Proficiency Bonus +4; Maneuver DC 18

Aberrant Recovery (Elite Trait, 1/Rest). When the aboleth is first bloodied, all conditions and effects it is suffering end for it, its elite traits activate, and all of its abilities recharge. Additionally, on its initiative count +10, or in place of an Action on its turn, the aboleth can use an elite action.

Amphibious. The aboleth can breathe air and water.

Aquatic. While underwater, the aboleth’s Dexterity score is 17 (+3), it is skilled in Acrobatics (+7), and it has advantage on melee attacks against creatures that do not have a swim speed.

Grasping Tentacles. If the aboleth hits the same target with two or more tentacle attacks on the same turn, the target is also grappled.

Mucous Cloud. While underwater, the aboleth is surrounded by transformative mucous. A creature that touches the aboleth or that hits it with a melee attack while within 5 feet if it must make a DC 15 Constitution saving throw. On a failure, the creature is diseased for 2 (1d4) hours. The diseased creature can breathe only underwater.

Probing Telepathy. If a creature communicates telepathically with the aboleth, the aboleth learns the creature’s greatest desires if the aboleth can see the creature.

Relentless. The aboleth has advantage on saving throws against spells and effects that would inflict the paralyzed, petrified, restrained, or stunned conditions.

ACTIONS
Multiattack. The aboleth makes three tentacle attacks.

Tentacle. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 13 (2d6 + 6) bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw or become diseased. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature’s skin become translucent and slimy, the creature can’t regain hit points unless it is underwater, and the disease can only be removed by heal or another disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes has passed.

Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

Dominate. The aboleth chooses one creature charmed by it and within 120 feet of it. The creature must make a DC 17 Intelligence saving throw or be dominated by the aboleth as in the spell dominate monster.

Psychic Slime (1/Short Rest). The aboleth fills the area in a 50-foot radius around it with a slimy mist. Creatures in the area, or that enter the area, must make a DC 15 Wisdom saving throw, taking 27 (6d8) psychic damage and is charmed by the aboleth on a failure, or half as much damage and not charmed on a success.

The slimy mist persists for 1 minute and an aboleth can use is swim speed in the area of the mist, even if the area is not in water. Additionally, creatures diseased by an aboleth can breathe the mist and regain hit points as if they where in water.

Enslave (3/Short Rest). The aboleth targets one creature it can see within 60 feet of it. The target must succeed on a DC 15 Wisdom saving throw or be magically charmed by the aboleth until the aboleth dies or until it is on a different plane of existence from the target. The charmed target is under the aboleth’s control and can’t take reactions, and the aboleth and the target communicate telepathically with each other over any distance.

Whenever the charmed target takes damage, the target can repeat the saving throw. On a success, the effect ends. No more than once every 24 hours, the target can also repeat the saving throw when it is at least one mile away from the aboleth.

BONUS ACTIONS
Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target grappled by the aboleth or incapacitated. Hit: 15 (2d8 + 6) piercing damage plus 3 (1d6) acid damage.

Invisibility (1/Short Rest). The, aboleth and one ally within 60 feet of it turn invisible, as in the spell greater invisibility, until the end of the aboleth’s next turn.

REACTIONS
Psychic Drain. If a creature ends its turn charmed by the aboleth, the aboleth can inflict 10 (3d6) psychic damage on the charmed creature, and the aboleth regains hit points equal to the damage the creature takes.

Tail Slap. If a creature ends its turn within 10 feet of the aboleth, the aboleth can make a tail attack targeting the creature.

ELITE ACTIONS
Detect. The aboleth can make a Wisdom (Perception) check.

Move. If the aboleth is underwater or in its psychic slime it can move half its speed without provoking opportunity attacks.

Tail Swipe. The aboleth makes one tail attack.

 

[dave2008]

Magestone: Aboleth by Osmatar

Aboleth Savant
Large aberration, lawful evil

Armor Class 18 (natural armor)
Hit Points 238 (28d10 + 84; bloodied 119)
Speed 10 ft., swim 50 ft.

STR	DEX	CON	INT	WIS	CHA
20 (+5)	8 (-1)	17 (+3)	22 (+6)	16 (+3)	20 (+5)

Savings Throws Dex +4, Int +11, Wis +8, Cha +10
Skills History +16, Insight +8, Perception +13, Persuasion +10
Damage Resistances acid, poison, psychic
Senses darkvision 120 ft., passive Perception 23
Languages Deep Speech, telepathy 180 ft.
Challenge 14 (11,500 XP) Proficiency Bonus +5

Amphibious. The aboleth can breathe air and water.

Aquatic. While underwater, the aboleth’s Dexterity score is 17 (+3), it is skilled in Acrobatics (+7), and it has advantage on melee attacks against creatures that do not have a swim speed.

Mucous Cloud. While underwater, the aboleth is surrounded by transformative mucous. A creature that touches the aboleth or that hits it with a melee attack while within 5 feet if it must make a DC 15 Constitution saving throw. On a failure, the creature is diseased for 2 (1d4) hours. The diseased creature can breathe only underwater.

Probing Telepathy. If a creature communicates telepathically with the aboleth, the aboleth learns the creature’s greatest desires if the aboleth can see the creature.

Relentless. The aboleth has advantage on concentration checks and saving throws against spells and effects that would inflict the paralyzed, petrified, restrained, or stunned conditions.

ACTIONS
Multiattack. The aboleth makes three attacks: two with its tentacles and one with its tail.

Tentacle. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 5) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Constitution saving throw or become diseased. While the creature is diseased it gains one level of exhaustion at the end of each of its turns. If the creature gains 6 levels of exhaustion it does not die. Instead, the diseased creature’s skin become translucent and slimy, the creature can’t regain hit points unless it is underwater, and the disease can only be removed by heal or another disease-curing spell of 6th level or higher. After this transformation the diseased creature removes on level of exhaustion for each round it is fully submerged in water. When the diseased creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes has passed.

Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage and the target must a DC 18 Strength saving throw or be pushed 10 feet.

Poison Spray. The aboleth extends a tentacle toward a creature it can see within 10 feet and projects a puff of noxious gas. The creature must make a DC 19 Constitution saving throw or take 19 (3d12) poison damage.

Enslave (3/Short Rest). The aboleth targets one creature it can see within 60 feet of it. The target must succeed on a DC 15 Wisdom saving throw or be magically charmed by the aboleth until the aboleth dies or until it is on a different plane of existence from the target. The charmed target is under the aboleth’s control and can’t take reactions, and the aboleth and the target communicate telepathically with each other over any distance.

Whenever the charmed target takes damage, the target can repeat the saving throw. On a success, the effect ends. No more than once every 24 hours, the target can also repeat the saving throw when it is at least one mile away from the aboleth.

Innate Spellcasting. The aboleth’s innate spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). It can innately cast the following spells, requiring no components:

At-will: hypnotic pattern
1/day each: mirage arcane, programmed illusion, project image

Spellcasting. The aboleth is a 14th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 19, +11 to hit with spell attacks). The aboleth has the following spells prepared:

Cantrips (at will): acid splash (11th level), mage hand, message, poison spray (11th level, refer to actions),, shocking grasp (11th level),
1st level (4 slots): arms of hadar, identify, magic missile, sleep, thunderwave, witch bolt
2nd level (3 slots): detect thoughts, locate object, melf’s acid arrow
3rd level (3 slots): clairvoyance, counterspell, dispel magic, fly, hunger of hadar
4th level (3 slots): arcane eye, banishment, phantasmal killer
5th level (2 slots): cloudkill, hold monster, scrying
6th level (2 slot): chain lightning, disintegrate
7th level (1 slot): prismatic spray

REACTIONS
Psychic Drain. If a creature ends its turn charmed by the aboleth, the aboleth can inflict 10 (3d6) psychic damage on the charmed creature, and the aboleth regains hit points equal to the damage the creature takes.

Retributive Casting. When a creature attacks the aboleth, the aboleth can cast an at-will spell targeting the creature that attacked it.

 

[dave2008]

Beholder by JamesBousema

Beholder Eye Tyrant
Large aberration, lawful evil

Armor Class 18 (natural armor)
Hit Points 199 (21d10 + 84; bloodied 99)
Speed 0 ft., fly 20 ft. (hover)

STR	DEX	CON	INT	WIS	CHA
12 (+1)	13 (+1)	19 (+4)	18 (+4)	15 (+2)	18 (+4)

Savings Throws Dex +6, Con +8, Int +9, Wis +7, Cha +9
Skills Arcana +9, History +9, Intimidation +9, Perception +12
Damage Resistances psychic
Condition Immunities prone
Senses darkvision 180 ft., passive Perception 22
Languages Deep Speech, Undercommon
Challenge 16 (15,000 XP) Proficiency Bonus +5

Aberrant Resistance. If the beholder fails a saving throw, it can use a reaction and re-roll the saving throw.

Antimagic Cone. The beholder’s central eye creates an area of antimagic, as in the antimagic field spell, in a 180-foot cone. At the start of each of its turns, the beholder decides which way the cone faces and whether the cone is active. The area works against the beholder’s own eye rays.

ACTIONS
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 14 (4d6) piercing damage.

Eye Rays. The beholder shoots three of the following magical eye rays, choosing one to three targets it can see within 120 ft. of it. Once it has selected an eye ray, it cannot use that ray again until the start of its next turn.

1. Charm Ray. The targeted creature must succeed on a DC 17 Wisdom saving throw or be charmed by the beholder for 1 hour, or until the beholder harms the creature.

2. Paralyzing Ray. The targeted creature must succeed on a DC 17 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success

3. Fear Ray. The targeted creature must succeed on a DC 17 Wisdom saving throw or be frightened for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

4. Slowing Ray. The targeted creature must succeed on a DC 17 Dexterity saving throw. On a failed save, the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

5. Enervation Ray. The targeted creature must make a DC 17 Constitution saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one.

6. Telekinetic Ray. If the target is a creature, it must succeed on a DC 17 Strength saving throw or the beholder moves it up to 30 ft. in any direction. It is restrained by the ray’s telekinetic grip until the start of the beholder’s next turn or until the beholder is incapacitated.

If the target is an object weighing 300 pounds or less that isn’t being worn or carried, it is moved up to 30 ft. in any direction. The beholder can also exert fine control on objects with this ray, such as manipulating a simple tool or opening a door or a container.

7. Sleep Ray. The targeted creature must succeed on a DC 17 Wisdom saving throw or fall asleep and remain unconscious for 1 minute. The target awakens if it takes damage or another creature takes an action to wake it. This ray has no effect on constructs and undead.

8. Petrification Ray. The targeted creature must make a DC 17 Dexterity saving throw. On a failed save, the creature begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is petrified until freed by the greater restoration spell or other magic.

9. Disintegration Ray. If the target is a creature, it must succeed on a DC 17 Dexterity saving throw or take 45 (10d8) force damage. If this damage reduces the creature to 0 hit points, its body becomes a pile of fine gray dust.

If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw. If the target is a Huge or larger object or creation of magical force, this ray disintegrates a 10-foot cube of it.

10. Death Ray. The targeted creature must succeed on a DC 17 Dexterity saving throw or take 55 (10d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

BONUS ACTIONS
Savage. The beholder can make a bite attack against a creature that is adjacent to it.

REACTIONS
Distant Dreams. When the beholder first drops below 110 hit points, it can teleport to an unoccupied space it can see within 120 feet of it.

LEGENDARY ACTIONS
The behodler can take 3 legendary actions, using the eye ray option below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Additionally, the beholder can use any unspent legendary actions at the end of the round and regains spent legendary actions at the start of its turn.

Eye Ray. The beholder uses an eye ray from the list of its available rays.

 

[dave2008]

Beholder Hive Mother by ???

Beholder Hive Mother
Huge aberration, lawful evil

Armor Class 20 (natural armor)
Hit Points 287 (25d12 + 125; bloodied 143)
Speed 0 ft., fly 20 ft. (hover)

STR	DEX	CON	INT	WIS	CHA
20 (+5)	12 (+1)	21 (+5)	20 (+5)	17 (+3)	18 (+4)

Savings Throws Str +11, Con +11, Int +11, Wis +9, Cha +10
Skills Arcana +11, History +11, Intimidation +10, Perception +15
Damage Resistances force, psychic
Condition Immunities prone
Senses darkvision 240 ft., passive Perception 25
Languages Deep Speech, Undercommon
Challenge 20 (25,000 XP) Proficiency Bonus +6

Aberrant Resistance. If the beholder fails a saving throw, it can use a reaction and re-roll the saving throw.

Antimagic Cone. The beholder’s central eye creates an area of antimagic, as in the antimagic field spell, in a 300-foot cone. At the start of each of its turns, the beholder decides which way the cone faces and whether the cone is active. The area works against the beholder’s own eye rays.

Hive Mother. The hive mother can cast, as a bonus action, dominate monster at-will against beholders and beholder-kin it can see within 180 feet of it. The hive mother does not need to concentrate to maintain control of dominated beholder kin and it can exert precise control as a bonus action. The hive mother can control a number of creatures whose total average hit points do not exceed 1000 and it has a telepathic link to the dominated creatures to a range of 10 miles. An unwilling beholder can resist a hive mothers control be succeeding on a DC 18 Wisdom saving throw and other hive mothers are immune to this effect.

Limited Magic Immunity. Unless the beholder wishes to be affected, it is immune to cantrips, and it is has advantage on saving throws against all other spells and magical effects and any creature that makes a spell attack against it has disadvantage on the attack roll.

ACTIONS
Multiattack. The hive mother makes up to four attacks: one Bite attack and three Eye Ray attacks.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 21 (3d10 + 5) piercing damage and the creature must make a DC 18 Strength saving throw or be grappled. A creature grappled in this way is also restrained.

Eye Rays. The beholder shoots a magical eye ray, choosing one target it can see within 180 ft. of it. Once it has selected an eye ray, it cannot use that ray again until the start of its next turn.

1. Charm Ray. The targeted creature must succeed on a DC 18 Wisdom saving throw or be charmed by the beholder for 2 hours, or until the beholder harms the creature.

2. Paralyzing Ray. The targeted creature must succeed on a DC 18 Constitution saving throw or be paralyzed for 2 minutes. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success

3. Fear Ray. The targeted creature must succeed on a DC 18 Wisdom saving throw or be frightened for 2 minutes. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

4. Slowing Ray. The targeted creature must succeed on a DC 18 Dexterity saving throw. On a failed save, the target’s speed is halved for 2 minutes. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

5. Enervation Ray. The targeted creature must make a DC 18 Constitution saving throw, taking 45 (10d8) necrotic damage on a failed save, or half as much damage on a successful one.

6. Telekinetic Ray. If the target is a creature, it must succeed on a DC 18 Strength saving throw or the beholder moves it up to 30 ft. in any direction. It is restrained by the ray’s telekinetic grip until the start of the beholder’s next turn or until the beholder is incapacitated.

If the target is an object weighing 800 pounds or less that isn’t being worn or carried, it is moved up to 40 ft. in any direction. The beholder can also exert fine control on objects with this ray, such as manipulating a simple tool or opening a door or a container.

7. Sleep Ray. The targeted creature must succeed on a DC 18 Wisdom saving throw or fall asleep and remain unconscious for 2 minutes. The target awakens if it takes damage or another creature takes an action to wake it. This ray has no effect on constructs and undead.

8. Petrification Ray. The targeted creature must make a DC 18 Dexterity saving throw. On a failed save, the creature begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is petrified until freed by the greater restoration spell or other magic.

9. Disintegration Ray. If the target is a creature, it must succeed on a DC 18 Dexterity saving throw or take 54 (12d8) force damage. If this damage reduces the creature to 0 hit points, its body becomes a pile of fine gray dust.

If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw. If the target is a Huge or larger object or creation of magical force, this ray disintegrates a 10-foot cube of it.

10. Death Ray. The targeted creature must succeed on a DC 18 Dexterity saving throw or take 66 (12d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

Spawn Beholder-kin (1/week). A piece of the hive mother drops off it and it suffers 75 hit points of damage. At the start of the hive mother's next turn the lump of flesh transforms into one of the following beholder-kin: 3d8 gazers, 1d8 spectators, 1d6 gauths, or 1 beholder. The beholder-kin act on its own initiative and is friendly to the hive mother for 1 minute and acts as her ally during this time.

REACTIONS
Distant Dreams. When the beholder is first bloodied, it can teleport to an unoccupied space it can see within 120 feet of it.

LEGENDARY ACTIONS
The beholder can take 3 legendary actions, using the eye ray option below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Additionally, the beholder can use any unspent legendary actions at the end of the round and regains spent legendary actions at the start of its turn.

Bite: The hive mother makes a bite attack.
Eye Ray. The hive mother uses an eye ray from the list of its available rays.
Move. The hive mother can move up to half its speed.
Regenerate. The hive mother regenerates 15 hit points
Swallow Whole (Costs 2 Actions). The hive mother makes a bite attack one a Large or smaller creature it has grappled. On a hit the creature is also swallowed. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the hive mother, and it takes 28 (8d6) acid damage at the start of each of its turns. If a creature is reduced to 0 hit points while swallowed, it dies and the hive mother regains 40 hit points.

If the hive mother dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 5 feet of movement, exiting prone.

 

[Stalker0]

Aboleth Savant
Large aberration, lawful evil
Challenge 14 (11,500 XP)
Amphibious. The aboleth can breathe air and water.

Now this thing is a beast! Honestly just the fact that when its attacked it can cast hypnotic pattern as a reaction is a really good defense. That plus the enslave means that a lot of the party is going to be in and out of this fight.

Just a few notes:

1) Tail: The proning effect feels weird because its primarily an underwater creature. Technically prone works underwater but I just find its a weird condition to use.

2) Disease: The diseases doesn't do much at this level...it would be nice to add a little more punch to them, and for them to kick in quicker

 

[Stalker0]

Beholder Hive Mother

Challenge 20 (25,000 XP)

I think 20 is over CRed for the monster. Comparing it to the Death Tyrant, its only real advantage is slightly more hp (which is nothing for that level), and the advantage on magic saves (which is almost normal at levels 16+ anyway).

The eye rays get a +1 DC and are slightly stronger, but not in the way that normally matters in a fight. The Death Tyrant was the real boost from the base beholder because of the ability to select the rays. But the Mother doesn't get that much more over the Tyrant. I could see CR 17, maybe 18....but this is mulch for a 20th level party.