Miastrilek

A constant spell affects the monster without the monster needing to cast it, and its duration is unlimited. If a constant spell gets counteracted, the monster can reactivate it by spending the normal spellcasting actions the spell requires.

The first time in a round that a creature within 30 feet of the miastrilek critically succeeds on a saving throw against a poison or disease or fully recovers from either such affliction via magic or another effect, the demon takes 6d6 mental damage.

The miastrilek can take on the appearance of any Small or Medium humanoid. This doesn't change their Speed but does prevent them from making fangs Strikes.

The miastrilek disgorges a spray of acid and rubble in a 30-foot cone, dealing 6d6 piercing and 6d6 acid damage (DC 30 reflex save). The area becomes hazardous terrain for 1 minute (2d6 acid damage). A creature can take this damage only once per turn. The miastrilek must wait 1d4 rounds before Spewing Pollution again.

Saving Throw DC 30 fortitude Maximum Duration 6 rounds Stage 1 –10-foot status penalty to all Speeds (1 round) Stage 2 –10-foot status penalty to all Speeds and a –1 circumstance penalty to attack rolls and checks requiring a firm grasp on held items (1 round) Stage 3 as Stage 2 , but increase the circumstance penalty to checks to –2 (1 round)