D&D 5E Setting Party level vs an Ancient Red Dragon

[Satyrn]

After nailing down players and doing research I have decided rather than use the Ancient Red, I am going to instead build a CR21 Red Dragon. That is the CR KFC says is deadly for 8 9th level PCs.

Using the Adult Red as a base, what suggestions do you have for increasing the CR to 21? How much does Legendary status and Lair increase the CR? What about some at will abilities to emulate those things?

Thanks.

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I'd give it more hit points so it can hang around another round or three

 

[Satyrn]

What about using, say, the Ancient Bronze as a base instead? I could just reskin it Red.

Speaking of, it seems odd versatility does not appear to be included in CR calculations. That is, the metallic dragon's multiple breath options does not seem to have any impact on their relative CR.

Aye, the offensive CR is essentially simplified down to DPR. I think mostly because versatility is rather impossible to measure - and besides, a couple breath weapon options is really barely more versatile than the many choices the dragon already has, with its various attacks other than the breath weapon.

As for the first question, I'd stick with the adult red and pump up its defensive CR with a boatload of hit points. My main concern would be having the dragon last long enough to be interesting.

 

[Tormyr]

What about using, say, the Ancient Bronze as a base instead? I could just reskin it Red.

Speaking of, it seems odd versatility does not appear to be included in CR calculations. That is, the metallic dragon's multiple breath options does not seem to have any impact on their relative CR.

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CR is calculated by using the highest possible damage option for 3 rounds.

 

[Reynard]

CR is calculated by using the highest possible damage option for 3 rounds.

That says quite a lot about the intent of the CR system, I guess. So how do you account for non-damaging effects that have a real impact like darkness or difficult terrain or even paralytic powers, etc...?

 

[Satyrn]

That says quite a lot about the intent of the CR system, I guess. So how do you account for non-damaging effects that have a real impact like darkness or difficult terrain or even paralytic powers, etc...?

You playtest it. The DMG says this.

That table in the DMG is only meant to be a starting point.

 

[Satyrn]

That says quite a lot about the intent of the CR system, I guess. So how do you account for non-damaging effects that have a real impact like darkness or difficult terrain or even paralytic powers, etc...?

Oh, and I'm forgetting that the DMG does list most if not all a few of the monster traits in the monster manual with a suggestion for how they affect the CR calculation.

 

[Tormyr]

That says quite a lot about the intent of the CR system, I guess. So how do you account for non-damaging effects that have a real impact like darkness or difficult terrain or even paralytic powers, etc...?

The DMG encounter building guidelines essentially suggest that you adjust the encounter difficulty a step one way or another if the environment or other factors beyond the monsters' CR affect the encounter.

I think they just considered that things got too confusing and had too many options to consider for a monster using a non-damaging ability. Even if a non-damaging ability is used that makes things difficult for the PCs, the monster is then not doing damage. Outside of a few monsters with lots of actions, teams of monsters, or monster abilities that remove a PC from the board, the PC generally recovers quickly, and the ability does not cause a loss of HP.

CR only gives a rough idea of a monsters power level / longevity in a fight. Encounter building guidelines roughly estimate the synergy in groups of PCs or monsters by adjusting the XP multiplier, but it cannot cover certain especially effective combinations.

 

[dave2008]

That says quite a lot about the intent of the CR system, I guess. So how do you account for non-damaging effects that have a real impact like darkness or difficult terrain or even paralytic powers, etc...?

The DMG provides a table that has many monster features and how they effect the CR. For example:

Magic Resistance: your increase its effective AC by 2 (essentially a +1 to defensive CR)

Legendary Resistance: adds to the creature's effective HP depending on level (30hp per use for epic monsters)

etc.

 

[Reynard]

Ok. So, if I use Kobold Fight Club as a guide and figure the correct CR for The Dragon is 22, I can start to build the creature.

Here is what the CR 24 Ancient Red Dragon Looks Like

Gargantuan dragon, chaotic evil

Armor Class 22 (natural armor)
Hit Points 546 (28d20 + 252)
Speed 40 ft., climb 40 ft., fly 80 ft.

STR DEX CON INT WIS CHA
30 (+10) 10 (+0) 29 (+9) 18 (+4) 15 (+2) 23 (+6)
Saving Throws Dex +7, Con +16, Wis +9, Cha +13
Skills Perception +16, Stealth +7
Damage Immunities fire
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 26
Languages Common, Draconic
Challenge 24 (62,000 XP)

Special Traits
Legendary Resistance (3/Day): If the dragon fails a saving throw, it can choose to succeed instead.
Actions
Multiattack: The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.
Bite: Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.
Claw: Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.
Tail: Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.
Frightful Presence: Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 21 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dragon’s Frightful Presence for the next 24 hours.
Fire Breath (Recharge 5–6): The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.
Legendary Actions
The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The dragon regains spent legendary actions at the start of its turn.

Detect: The dragon makes a Wisdom (Perception) check.
Tail Attack: The dragon makes a tail attack.
Wing Attack (Costs 2 Actions): The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

and here is what a CR 22 Ancient Green Dragon looks like:

Gargantuan dragon, lawful evil

Armor Class 21 (natural armor)
Hit Points 385 (22d20 + 154)
Speed 40 ft., fly 80 ft., swim 40 ft.

STR DEX CON INT WIS CHA
27 (+8) 12 (+1) 25 (+7) 20 (+5) 17 (+3) 19 (+4)
Saving Throws Dex +8, Con +14, Wis +10, Cha +11
Skills Deception +11, Insight +10, Perception +17, Persuasion +11, Stealth +8 Damage Immunities poison Condition Immunities poisoned
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 27
Languages Common, Draconic
Challenge 22 (41,000 XP)

Special Traits
Amphibious: The dragon can breathe air and water.
Legendary Resistance (3/Day): If the dragon fails a saving throw, it can choose to succeed instead.
Actions
Multiattack: The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.
Bite: Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 10 (3d6) poison damage.
Claw: Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 22 (4d6 + 8) slashing damage.
Tail: Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.
Frightful Presence: Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 19 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dragon’s Frightful Presence for the next 24 hours.
Poison Breath (Recharge 5–6): The dragon exhales poisonous gas in a 90-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 77 (22d6) poison damage on a failed save, or half as much damage on a successful one.
Legendary Actions
The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The dragon regains spent legendary actions at the start of its turn.

Detect: The dragon makes a Wisdom (Perception) check.
Tail Attack: The dragon makes a tail attack.
Wing Attack (Costs 2 Actions): The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

The biggest differences are in claw damage output, breath weapon damage, and a HUGE number of hit points. The Green has far more skills but I am not sure that matters. If I give the dragon spells there's some difference there too.

 

[Reynard]

The stage is finally set. It looks like tomorrow night the adventure begins. I don't know how quickly the party will have their first engagement with the dragon. They are arriving in the middle of what is effectively an apocalyptic war. The Dragonborn have been revealed as "sleeper" agents of the dragon and are doing post-conflagaration clean-up and control. The major cities have been emptied and the people are begging the fae for shelter while a loose alliance of the surviving human kingdoms, former orc slaves and others are trying to maintain some control and fight off the dragonborn. The last bastion of actual civilization is the magic academy whose wards have so far kept the dragon at bay, but the most powerful wizards left for other lands and worlds years before. If the PCs kill the dragon then the dragonborn will be free willed once again and the war will likely end.

The High King that was killed a decade ago when the Dragon returned became High King by (apparently) slaying the dragon and taking its hoard. What no one knows is that the High King used an artifact spear the "kill" the Dragon -- actually putting it in stasis as long as the spear remained in the Dragon's heart. The queen of the elf Spring Court granted the High King the spear in the first place but ten years ago the Winter Queen took the spear back, causing the Dragon to return. There are just enough hints about the elf involvement in this mess the PCs might go there first, either to beg aid or take back the spear.