Eye Monger

Magical effects, including those produced by spells and magic items but excluding those created by artifacts or deities, are suppressed inside the eye monger's gullet. Any spell slot or charge expended by a creature in the gullet to cast a spell or activate a property of a magic item is wasted. While an effect is suppressed, it doesn't function, but the time it spends suppressed counts against its duration. No spell or magical effect that originates outside the eye monger's gullet, except one created by an artifact or a deity, can affect a creature or an object inside the gullet.

If the eye monger is motionless and has its eye and mouth closed at the start of combat, it has advantage on its initiative roll. Moreover, if a creature hasn't observed the eye monger move or act, that creature must succeed on a DC 18 Intelligence (Investigation) check to discern that the eye monger is animate.

The eye monger doesn't require air.

Melee Weapon Attack +9 to hit, reach 5 ft., one target. 12 (2d6 + 5) Piercing damage, and if the target is a Medium or smaller creature, it must succeed on a DC 18 Dexterity saving throw or be swallowed by the eye monger and deposited in the eye monger's gullet (see Antimagic Gullet). The eye monger can swallow one creature at a time. A swallowed creature is Blinded and Restrained, has Cover against attacks and other effects originating outside the eye monger, and takes 35 (10d6) Acid damage at the start of each of its turns.
If the eye monger takes 25 damage or more on a single turn from a creature inside its gullet, the eye monger regurgitates the swallowed creature, which falls Prone in a space within 10 feet of the eye monger. If the eye monger dies, a swallowed creature is no longer Restrained by it and can escape from the corpse by using 10 feet of movement, exiting Prone.