Here is a more challenging and interesting to run Yestabrod for your Out of the Abyss campaign.
Rot Priest of Zuggtmoy
|Large monstrosity, chaotic evil
Armor Class 15 (natural armour)
Damage Immunities poison
Legendary Resistance (1/day). If Yestabrod fails a saving throw, it can choose to succeed instead.
Slam. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 6 (1d6+3) piercing damage. The target must succeed on a DC 13 Constitution saving throw or be poisoned for 1 hour. If the saving throw fails by 5 or more, the target is also unconscious while poisoned in this way. The target wakes up if it takes damage or if another creature takes an action to shake it awake.
Caustic Spores (1/day). Yestabrod releases spores in a 30-foot cone. Each creature in that area must succeed on a DC 12 Dexterity saving throw or take 1d10+3 acid damage and ongoing 5 acid damage at the start of each of Yesiabrod’s turns. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Infestation Spores (1/day). Yestabrod releases spores that burst out in a cloud that fills a 10-foot-radius sphere centred on it, and the cloud lingers tor 1 minute. Any flesh-and-blood creature in the cloud when it appears, or that enters it later, must make a DC 12 Constitution saving throw, on a successful save, the creature can’t be infected by these spores for 24 hours. on a failed save, the creature is infected with a disease called the spores of Zuggtmoy and also gains a random form indefinite madness (determined by rolling on the Madness of Zuggtmoy table in appendix D) that lasts until the creature is cured of the disease or dies.
While infected in this way, the creature can’t be reinfected, and it must repeat the saving throw at the end of every 24 hours, ending the infection on a success. On a failure, the infected creature’s body is slowly taken over by fungal growth, and after three such failed saves, the creature dies and is reanimated as a spore servant if it’s a type of creature that can be (see the “Myconids” entry in the Monster Manual
Yestabrod can take 2 legendary actions, choosing from the options below. Only one legendary option can be used at a time and only at the end of another creature’s turn. Yestabrod regains spent legendary actions at the start of her turn.
- Corpse Explosion. Gore, offal, and acid erupt from a corpse within 20 Feet of Vestabrod. Creatures within l0 feet of the corpse must succeed on a DC 12 Dexterity saving throw or take 3d4+2 acid damage
- Foul Absorption. Yestabrod absorbs putrescence from a corpse within 5 feet of it, regaining 2d4+2 hit points.
A disgusting larval creature rises up before you, showing only vestigial fungal growths that hint that it might once have been a myconid