D&D 5E Homebrew Monster: Prismatic Hydra

Caliban

Rules Monkey
This is a legendary hydra I plan on having my players encounter in our next session. Thought I'd share it in case anyone found it interesting. It will be at the bottom of a 30' deep body of water, with the PC's on platforms and walkways that are 10' above the surface of the water.

Prismatic Hydra


Type:
Monstrosity
Size: Gargantuan
Speed: 30 ft., swim 30 ft.
AC: 15 (Natural Armor)
HP: 230 (20d12+100)
Alignment: Chaotic Neutral
Challenge Rating:11

STRDEXCONINTWISCHA
20 (+5)20 (+5)20 (+5)2 (-4)107 (-2)

Skills: Perception +6
Passive Perception: 16
Senses: Darkvision 60 Ft.


Traits
Feat: Warcaster (allows it to use a beam attack as an opportunity attack)
Legendary Resistance (3/Day):If the hydra fails a saving throw, it can choose to succeed instead.
Immunities: Disease
Resistances: Each head is resistant to the type of damage it can do.
Hold Breath: The hydra can hold its breath for 1 hour.
Multiple Heads:The hydra has five heads. (Choose or roll on the Hydra Head chart to see which colors it starts with, While it has more than one head, the hydra has advantage on saving throws against being Blinded, Charmed, Deafened, Frightened, Stunned, and knocked Unconscious.

Whenever the hydra takes 25 or more damage in a single turn, one of its heads dies. If all its heads die before its turn, the prismatic hydra will blindly flee (usually underwater) and attempt to retreat into an underwater burrow and hibernate until it can regrow its heads.

At the end of its turn, it grows two heads for each of its heads that died since its last turn. Roll on the Hydra Head chart for each head to see what type of head regrows. The hydra regains 10 hit points for each head regrown in this way. (All extra heads are reabsorbed into the hydra’s body at the end of a long rest.)

Independant Heads:
The heads can be targeted individually, and all take damage individually if they are caught in the same AoE effect. They are considered Large creatures. The heads all share the same HP pool. The Prismatic Hydra prefers to stays submerged at least 10’ below the water during combat, but as each of its heads has a 30’ long neck and a 60’ range eyebeam, this is usually not a hindrance. The heads are somewhat chaotic in nature and do not usually exhibit teamwork or focus their attacks unless there is only one target.

Reactive Heads:
For each head the hydra has beyond one, it gets an extra reaction that can be used only for Opportunity Attacks.

Wakeful:
While the hydra sleeps, at least one of its heads is awake.

Prismatic Heads: Each head can shoot a beam of energy from its mouth instead of making a bite attack. Dexterity Save DC: 17, full effect on a failed save, no effect on a successful save. Range: 60’

Hydra Head Chart:

Head ColorDamage ResistancePrevents Head RegrowthEffect on a Failed Save
1) RedFireCold damage10d6 fire damage
2) OrangeAcidLightning damage10d6 acid damage
3) YellowLightningAcid damage10d6 lightning damage
4) GreenPoisonAny effect that fixes he poisoned condition10d6 poison damage
5) BlueColdFire damage10d6 cold damage
6) IndigoSlashing/ PiercingThunder damageRestrained. New Con save at end of turn: 3 failures = Petrified/3 successes ends effect
7) VioletForceNecrotic damageBlinded. New Wis save at beginning of turn. Failure = transported to Digestion Dimension. (See below)
8) BlackNecroticRadiant damage10d6 necrotic damage
9) GrayNecroticRadiant damageAnimate Dead (Can animate severed hydra heads as undead giant constrictor snakes, size large instead of huge)
10) WhiteRadiantNecrotic damgae10d6 radiant damage
Digestion Dimension: a pocket dimension that can store up to 16 medium creatures or 4 large creatures or 1 huge creature. The walls of the digestion dimension feel like living flesh coated in digestive juices. Creatures in the digestion dimension take 5d6 acid damage (con save for half) at the beginning of each of their turns. Dealing 25 points of damage in one turn to the walls of the digestion dimension causes a rupture that will expel one creature out of the dimension via the violet hydra’s mouth. Dealing 50 points of damage to the walls of the digestion dimension will collapse the dimensions, destroying the violet hydra head and expelling all creatures via the neck stump. Likewise, dealing 25 point of damage the violet hydra head from outside will severe the head, collapse the dimension, and expel the contents of the dimension via the neck stump.

Actions

Multiattack:
The hydra makes as many bite attacks as it has heads. It may replace up to 3 bite attacks with beam attacks on different targets (only targeting the same creature if no other targets are available) - the heads work independently and don’t use teamwork

Bite: Melee Weapon Attack: +9 to hit, reach 30 ft. (effectively 20 ft as the main body stays submerged 10’ below water), one target.
Hit: 10 (1d10 + 5) piercing damage.
Legendary Actions

Can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary actions are regained at the start of each turn.

Beam Attack: One head that has not made a beam attack since the beginning of the hydra’s last turn can make a beam attack against a random enemy.

Bite Attack:
May make a bite attack against a random enemy within range.

Regrow Head (costs 2 actions):If the hydra currently has less than 5 heads, it may immediately regrow a head and heal 10 hit points.

 

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Olrox17

Hero
Going purely by the numbers, this monster should be around CR 18-19. Given the lack of teamwork between the heads (no focus fire tactics), I could see a CR 16, 15 at the lowest, as appropriate. CR 11 seems a bit too low.
 

S

Sunseeker

Guest
Going purely by the numbers, this monster should be around CR 18-19. Given the lack of teamwork between the heads (no focus fire tactics), I could see a CR 16, 15 at the lowest, as appropriate. CR 11 seems a bit too low.

But with that 15AC, it will be almost impossible to miss. It sort of depends on the party here. If the heads are "conveniently close" to the platforms, and the hydra plays smart (hydras are not typically smart) then a martial-heavy party can chew through 230 HP in about 4 rounds. If melee can't reach the heads then the AC is irrelevant and its up to the casters to say "Oh! Better not shoot fire at the red head!" I'd give it ~8 rounds.
 

Olrox17

Hero
But with that 15AC, it will be almost impossible to miss. It sort of depends on the party here. If the heads are "conveniently close" to the platforms, and the hydra plays smart (hydras are not typically smart) then a martial-heavy party can chew through 230 HP in about 4 rounds. If melee can't reach the heads then the AC is irrelevant and its up to the casters to say "Oh! Better not shoot fire at the red head!" I'd give it ~8 rounds.

According to the most recent encounter guidelines, a 6th or 7th level party of five PCs should be able to beat a CR 11 legendary monster. I'm pretty sure a normal party of that level can't take this hydra. If we're assuming extreme optimization, then CRs do not matter at all.
 

S

Sunseeker

Guest
According to the most recent encounter guidelines, a 6th or 7th level party of five PCs should be able to beat a CR 11 legendary monster. I'm pretty sure a normal party of that level can't take this hydra. If we're assuming extreme optimization, then CRs do not matter at all.

5E CR guidelines are soft. I don't think extreme optimization needs to be assumed here at all, plus there's not much room for optimization from levels 6-11. There just isn't, and you don't even have access to the "big guns" of magic either.

A party of 5 fighters (who are neither complete morons nor total optimizers) could take this monster down in 5 rounds. They're going to dish out ~15 points per fighter, per turn, that's ~75 points per round, accounting for peaks thanks to Action Surge and crits and valleys from misses. At level 6 they will have a proficiency of +3, assuming they maxed their attack/damage stat that's +8 to hit minimum, so they only need to roll a 7 to hit.

The biggest danger here is the breath weapons, and the risk of melee-types simply not being in damage range. If your party is clever and the hydra is stupid, you can even get the heads to hit each other and 10d6 will, on average, nuke any other head.

So again, I'd give this monster about 5 rounds.
 

Quickleaf

Legend
This is a legendary hydra I plan on having my players encounter in our next session. Thought I'd share it in case anyone found it interesting. It will be at the bottom of a 30' deep body of water, with the PC's on platforms and walkways that are 10' above the surface of the water.

Prismatic Hydra


Type:
Monstrosity
Size: Gargantuan
Speed: 30 ft., swim 30 ft.
AC: 15 (Natural Armor)
HP: 230 (20d12+100)
Alignment: Chaotic Neutral
Challenge Rating:11

STRDEXCONINTWISCHA
20 (+5)20 (+5)20 (+5)2 (-4)107 (-2)

Skills: Perception +6
Passive Perception: 16
Senses: Darkvision 60 Ft.


Traits
Feat: Warcaster (allows it to use a beam attack as an opportunity attack)
Legendary Resistance (3/Day):If the hydra fails a saving throw, it can choose to succeed instead.
Immunities: Disease
Resistances: Each head is resistant to the type of damage it can do.
Hold Breath: The hydra can hold its breath for 1 hour.
Multiple Heads:The hydra has five heads. (Choose or roll on the Hydra Head chart to see which colors it starts with, While it has more than one head, the hydra has advantage on saving throws against being Blinded, Charmed, Deafened, Frightened, Stunned, and knocked Unconscious.

Whenever the hydra takes 25 or more damage in a single turn, one of its heads dies. If all its heads die before its turn, the prismatic hydra will blindly flee (usually underwater) and attempt to retreat into an underwater burrow and hibernate until it can regrow its heads.

At the end of its turn, it grows two heads for each of its heads that died since its last turn. Roll on the Hydra Head chart for each head to see what type of head regrows. The hydra regains 10 hit points for each head regrown in this way. (All extra heads are reabsorbed into the hydra’s body at the end of a long rest.)

Independant Heads:
The heads can be targeted individually, and all take damage individually if they are caught in the same AoE effect. They are considered Large creatures. The heads all share the same HP pool. The Prismatic Hydra prefers to stays submerged at least 10’ below the water during combat, but as each of its heads has a 30’ long neck and a 60’ range eyebeam, this is usually not a hindrance. The heads are somewhat chaotic in nature and do not usually exhibit teamwork or focus their attacks unless there is only one target.

Reactive Heads:
For each head the hydra has beyond one, it gets an extra reaction that can be used only for Opportunity Attacks.

Wakeful:
While the hydra sleeps, at least one of its heads is awake.

Prismatic Heads: Each head can shoot a beam of energy from its mouth instead of making a bite attack. Dexterity Save DC: 17, full effect on a failed save, no effect on a successful save. Range: 60’

Hydra Head Chart:

Head ColorDamage ResistancePrevents Head RegrowthEffect on a Failed Save
1) RedFireCold damage10d6 fire damage
2) OrangeAcidLightning damage10d6 acid damage
3) YellowLightningAcid damage10d6 lightning damage
4) GreenPoisonAny effect that fixes he poisoned condition10d6 poison damage
5) BlueColdFire damage10d6 cold damage
6) IndigoSlashing/ PiercingThunder damageRestrained. New Con save at end of turn: 3 failures = Petrified/3 successes ends effect
7) VioletForceNecrotic damageBlinded. New Wis save at beginning of turn. Failure = transported to Digestion Dimension. (See below)
8) BlackNecroticRadiant damage10d6 necrotic damage
9) GrayNecroticRadiant damageAnimate Dead (Can animate severed hydra heads as undead giant constrictor snakes, size large instead of huge)
10) WhiteRadiantNecrotic damgae10d6 radiant damage
Digestion Dimension: a pocket dimension that can store up to 16 medium creatures or 4 large creatures or 1 huge creature. The walls of the digestion dimension feel like living flesh coated in digestive juices. Creatures in the digestion dimension take 5d6 acid damage (con save for half) at the beginning of each of their turns. Dealing 25 points of damage in one turn to the walls of the digestion dimension causes a rupture that will expel one creature out of the dimension via the violet hydra’s mouth. Dealing 50 points of damage to the walls of the digestion dimension will collapse the dimensions, destroying the violet hydra head and expelling all creatures via the neck stump. Likewise, dealing 25 point of damage the violet hydra head from outside will severe the head, collapse the dimension, and expel the contents of the dimension via the neck stump.

Actions

Multiattack:
The hydra makes as many bite attacks as it has heads. It may replace up to 3 bite attacks with beam attacks on different targets (only targeting the same creature if no other targets are available) - the heads work independently and don’t use teamwork

Bite: Melee Weapon Attack: +9 to hit, reach 30 ft. (effectively 20 ft as the main body stays submerged 10’ below water), one target.
Hit: 10 (1d10 + 5) piercing damage.
Legendary Actions

Can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary actions are regained at the start of each turn.

Beam Attack: One head that has not made a beam attack since the beginning of the hydra’s last turn can make a beam attack against a random enemy.

Bite Attack:
May make a bite attack against a random enemy within range.

Regrow Head (costs 2 actions):If the hydra currently has less than 5 heads, it may immediately regrow a head and heal 10 hit points.


Interesting monster! Having run a hydra fight not long ago (and for a homebrew "pyrohydra" too), I think it looks fun. :)

How do you handle individual head resistances though? Do you intend to require players to choose which head they're attacking? What if a player says "I attack its body"?

Hmm...and CR 11 looks off to me...let me run quick monster maths...

...assuming it uses Legendary Actions to regrow a head + beam attack each round for a 3-round fight.

Defense CR = 13
HP 230 + 30 regrow heads = 260
AC 15 + 2 legendary resistances = 17

Offense CR = 21

DPR (3-rounds)
Round #1) assume it loses one head & regrows one head - has 5 heads; Prismatic Heads ( 5 * 35 damage ) + Legendary Action: Beam Attack ( 35 damage ) = 210 dmg
Round #2) assume it loses two heads & regrows one head - has 4 heads; Prismatic Heads ( 4 * 35 damage ) + Legendary Action: Beam Attack ( 35 damage ) = 175 dmg
Round #3) assume it loses two heads & regrows one head - has 3 heads; Prismatic Heads ( 3 * 35 damage ) + Legendary Action: Beam Attack ( 35 damage ) = 140 dmg

DPR = (210 + 175 + 140) / 3 = 175

That's CR 22. But Save DC 17 drops it down to CR 21. And that's ignoring Pocket Dimension & multi-opportunity attack damage!

Total CR = 17

Definitely not a CR 11 critter.
 

Caliban

Rules Monkey
I'm not too concerned about the CR rating, but the hydra may be a bit tougher than I want it to be. They didn't end up encountering it today, instead getting sidetracked with a side quest to acquire a premium pet carrier for the monk's pet Tressym (only 10,000 gp for a top of the line adventure ready pet carrier).

They should encounter it next session. The party is 5 level 8 PC's (Tiefling Fighter/Bladelock, Elven Wizard-Bladesinger, Aasimar Open-Palm Monk, Human Valor Bard, and a black Dragonborn Rogue-Shadowscale (homebrew rogue archtype). They have some good gear, including several non-standard magic items, and everyone has an extra feat. So they are tougher than a standard lvl 8 party, and I make the elite monsters stronger as well (regular MM monsters are usually just mooks for the elite versions).

I may reduce the damage of the beam attacks. Or maybe I'll just run it as-is and see if they are smart enough to retreat if it gets too dangerous for them.
 

S

Sunseeker

Guest
I'm not too concerned about the CR rating, but the hydra may be a bit tougher than I want it to be. They didn't end up encountering it today, instead getting sidetracked with a side quest to acquire a premium pet carrier for the monk's pet Tressym (only 10,000 gp for a top of the line adventure ready pet carrier).

They should encounter it next session. The party is 5 level 8 PC's (Tiefling Fighter/Bladelock, Elven Wizard-Bladesinger, Aasimar Open-Palm Monk, Human Valor Bard, and a black Dragonborn Rogue-Shadowscale (homebrew rogue archtype). They have some good gear, including several non-standard magic items, and everyone has an extra feat. So they are tougher than a standard lvl 8 party, and I make the elite monsters stronger as well (regular MM monsters are usually just mooks for the elite versions).

I may reduce the damage of the beam attacks. Or maybe I'll just run it as-is and see if they are smart enough to retreat if it gets too dangerous for them.

Personally, I'd keep the beam weapons as is. While I think the party would make quick work of it due to low AC and low HP, (especially the party you just described) those breath weapons are quite the doozy at that level. Plus you've got at least 4 party members with good Dex saves (Bladelock, Blaesinger, Monk & Rogue).

If I had any suggestions, I'd add another 50HP, minimum, 100 tops.
 

Caliban

Rules Monkey
Interesting monster! Having run a hydra fight not long ago (and for a homebrew "pyrohydra" too), I think it looks fun. :)

How do you handle individual head resistances though? Do you intend to require players to choose which head they're attacking? What if a player says "I attack its body"?

For the most part I plan on treating the heads as Large creatures that share a HP pool. The player attacks whichever head they choose that is within reach of their attack.

If they want to attack the body, it is under 10' of murky water (heavy obscurement, underwater combat rules, and most ranged attacks fired into the water will simply be absorbed by the water). But it will have none of the resistances of the various heads. They will still end up cutting off a random head if they do more than 25 pts of damage (the necks are always writhing around and getting in the way...)
 

Caliban

Rules Monkey
Personally, I'd keep the beam weapons as is. While I think the party would make quick work of it due to low AC and low HP, (especially the party you just described) those breath weapons are quite the doozy at that level. Plus you've got at least 4 party members with good Dex saves (Bladelock, Blaesinger, Monk & Rogue).

If I had any suggestions, I'd add another 50HP, minimum, 100 tops.

I'll probably run it as written, and add some HP if they are having too easy a time of it. I want it to be a challenge, but I don't want it to be a long boring fight. It should live long enough for each of the PC's to do at least one cool thing, and have some scary moments if they fail too many saves.
 

S

Sunseeker

Guest
I'll probably run it as written, and add some HP if they are having too easy a time of it. I want it to be a challenge, but I don't want it to be a long boring fight. It should live long enough for each of the PC's to do at least one cool thing, and have some scary moments if they fail too many saves.

I do hope you get to spawn some of those more unique heads down the list. I think that'll really take your party for a spin.
 


Olrox17

Hero
5E CR guidelines are soft. I don't think extreme optimization needs to be assumed here at all, plus there's not much room for optimization from levels 6-11. There just isn't, and you don't even have access to the "big guns" of magic either.

A party of 5 fighters (who are neither complete morons nor total optimizers) could take this monster down in 5 rounds. They're going to dish out ~15 points per fighter, per turn, that's ~75 points per round, accounting for peaks thanks to Action Surge and crits and valleys from misses. At level 6 they will have a proficiency of +3, assuming they maxed their attack/damage stat that's +8 to hit minimum, so they only need to roll a 7 to hit.

The biggest danger here is the breath weapons, and the risk of melee-types simply not being in damage range. If your party is clever and the hydra is stupid, you can even get the heads to hit each other and 10d6 will, on average, nuke any other head.

So again, I'd give this monster about 5 rounds.
I believe you are underestimating the hydra's damage numbers (read Quickleaf's post for details). In any case, now we know that the OP's group is level 8, which should be enough to take down this thing (unless they spend too many resources before fighting it).
 

Caliban

Rules Monkey
I believe you are underestimating the hydra's damage numbers (read Quickleaf's post for details). In any case, now we know that the OP's group is level 8, which should be enough to take down this thing (unless they spend too many resources before fighting it).

Quickleaf seems to assume everyone is going to fail their saves against every single beam attack, every round. Not likely. I set the damage to be "all or nothing" - either you get hit by the beam or you don't.

Plus, the prismatic heads won't target the same creature (too chaotic) so the damage will be spread out (unless only one PC is available as a target).

Additionally - only three heads can use beam attacks on it's turn, the other two will bite. It needs to use legendary actions to get more beam attacks.

It should be a tough fight, and I may have overestimated how well my players will do, but I think it's within their capabilities.
 

Caliban

Rules Monkey
I ran the encounter tonight - it was in 100' x 100' room with several 10' x 10' platforms and catwalks around the edges and "pump controls" in the center of the room. The room was a central processing point and pumping station for trash and sewage in a massive sewer complex under the city. The hydra had taken up residence and city was unable to access the pump controls or the room itself, and trash sewage was piling up.

As they fought the hydra, if they dodged a beam attack it would take out a nearby portion of the platform or catwalk they were standing on, diminishing the available area to fight on.

The body of the hydra was under 10' of water, and the water was 10' below the platforms. They could have made it too the pumping station controls to lower the water level and expose the hydra's body, but they didn't think of it.

For the first two rounds they were certain I was trying to TPK them, partially due to several poor rolls on their part. But the Elven wizard bladesinger cast Haste on himself (Advantage on Dex saves), the bard turned himself invisible (for this combat I ruled it would give him advantage on Dex saves vs the beams because he was harder to target), the Aasimar monk and Dragonborn rogue just relied on their naturally high Dex saves, and the Tiefling fighter/warlock just had to tough it out and save his "Dark One's Own Luck".

I tried several times, but failed to send anyone to the Digestion Dimension (the Rogue failed herDex save twice, but made the Wisdom save once, and the Bard used Dispel Magic to end the effect before she was send to the DD - and the Fighter Warlock expended Bardic Inspiration and Dark One's Own Luck to avoid it.)

They focused on killing heads and not allowing them to regrow naturally - they killed about 7 heads, but only one was able to regrow two new heads, the other heads I had to use Legendary Actions to replace. At one point they had it down to a single head, then it regrew two and used Legendary actions to regrow another.

The finishing blow was dealt by the bard, with Vicious Mockery when it had 3 heads left. I described it as being so confused by the insult that the heads stared at each other in confusion, then one by one their heads exploded as it was unable to process it's conflicting emotions. Several PC's were bloodied, and the bladesinger was taken to zero HP just before they killed the hydra. (I did end up giving the hydra another 50 HP for the fight.)

Overall, I think it was a success.
 

Stalker0

Legend
I feel like the hydra is a bit too vulnerable to area effects. Heck a decent fireball could knock out all heads without fire resistance in one go.
 

Caliban

Rules Monkey
I feel like the hydra is a bit too vulnerable to area effects. Heck a decent fireball could knock out all heads without fire resistance in one go.
That's why I made the room so big. The heads each take up a 10x10 area and spread out, and move around every turn.

The wizard was able to get two of them in a fireball, once. They could have gotten three at one point, and another time four heads were lined up for a lightning bolt but they weren't able to capitalize on it.

Sent from my SAMSUNG-SM-G930A using EN World mobile app
 

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