Carnifex

Aura of Pestilence. Each creature within 30ft of the Carnifex takes 2d6 poison damage when they start their turn within the aura or step into it for the first time.  

Multi Headed. This creature has 4 total heads that can be targeted by single target spells individually, spells like blindness/deafness, Command, etc. Only take effect on the subsequent head. Each head has advantage against the unconscious, blinded, and deafened conditions. A head can be severed from the Carnifex with a Silvered weapon dealing more than 25 damage in a single hit. This can be done until there is one head left in which the body will spontaneously regrow 1d4 heads at the end of its next turn. If all of its heads are severed it becomes immune to the following conditions and damages: blinded, charmed, stunned, deafened, thunder, frightened. If all of the heads are decapitated then any of the previous effects are automatically ended. 

Reactive. The Carnifex can make as many opportunity attacks for as many heads it has. 

Spiny hide. Each time a creature hits the Carnifex with an attack while within 5ft they take an additional 3d4 piercing damage. 

Horrific Regeneration (2/Day). When this creature would have dropped to 0 hit points it instead is set to 80 hit points and gains an additional 10 hit points at the start of its next three turns. 

Horrific Rat. This creature gains 1 additional turn during combat equal to 10-(initiative count). On this turn a creature can use a bonus action, reaction, and if there is 1 or more creatures of lower CR with this trait that can see this creature it can make 1 attack regardless of any traits or affects giving them multiple attacks. The attack must target a single creature. On this turn a creature does not regain and cannot use recharge abilities or legendary actions. Additionally if this creature has legendary resistances, it can forgo this trait for 1 day and regain all expended uses of legendary resistances. 

Multi headed. The Carnifex can make as many bite attacks as it has heads, it can substitute one use of a bite attack for a use of breath weapon. 

Breath Weapon. The Carnifex being multi headed has access to the following breath weapons. Only 1 breath weapon can be used at a time. When each breath weapon has been used, it cannot be regained until all the breath weapons have been expended. 

• Noxious Breath. Each creature caught in a 30ft cone must make a DC 18 DEX save or take 35 (10d6) necrotic damage and gains 1 level of contamination. If a creature fails this save by 10 or more they gain the weakened condition for 1 hour (save ends). Success: half damage and no contamination.
• Rotting Breath. Each creature caught in a 40ft by 5ft line must make a DC 18 WIS save or gain the poisoned and slowed condition and takes 38 (7d10) poison damage. If a creature fails this save by 10 or more they gain the shocked condition for 1 hour (save ends). 
• Exhausting Breath. Each creature in a 20ft radius emanating from the carnifex must make a DC 18 CON saving throw or gain the poisoned condition, while poisoned in this way a creature is slowed and has the frightened condition. Additionally take 40 (9d8) psychic damage. If a creature fails this save by 10 or more they gain 1 level of exhaustion. Success: half damage and not poisoned. 
• Chromatic Breath. Each creature caught in a 90ft by 5ft line must make a DC 18 STR save or take 52 (15d6) cold damage and gain the frozen condition (DC 18 Athletics check). Success: half damage only. 

Bite. Melee Attack Roll: +12 to hit, reach 5ft., 1 target. Hit: 24 (4d6+10) piercing damage and gains the prone condition. 

The Carnifex has 3 legendary actions choosing from the list below. Only one action can be used at a time at the end of another creatures turn. Regaining all expended uses at the start of its next turn. 

Wing attack (Costs 2 actions). The Carnifex forces each creature within a 30ft radius to make a DC 15 DEX save or be knocked prone as it flies into the air up to its movement speed. This movement does not provoke opportunity attacks. 

Bite. The carnifex uses its bite attack.