Ammut's Heart

False Appearance. When Ammut's Heart is motionless, it is indistinguishable from other fungi.  

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a shroom the fit through. The swarm can't regain hit points or gain temporary hit points.

Death Burst.  The gas spore explodes when Ammut's Heart drops to 0 HP.  Any creature in a 20-foot radius must succeed on a DC 15 Con save or take 9 (3d6) poison damage and become infected with a madness.  Roll a d4.  On a 1-2 roll on the short term madness table, on a 3-4 roll on the long term madness table.  Any creature with poison immunity will not be affected by a madness.  

Bite. Melee Weapon Attack: +2 to hit, reach 0 ft., one target in the swarm's space. Hit: 7 (2d6+1) piercing damage, or 3 (1d6) piercing damage if the swarm has half of its hit points or fewer and takes 4 (d8) poison damage on a successful hit.

Hallucination Spores.  Target one creature. Reach 5 feet.  The target must succeed on a DC 12 Con saving throw or be poisoned for 1 minute.  The poisoned target is incapacitated while it hallucinates.  The target can repeat the saving throw at the end of its turn.  On a successful save the hallucination ends.

Touch (1/Long Rest).  Melee Weapon Attack:  +2 to hit.  Reach 0 ft.  One Target in the swarm's space.  2 (d4) poison damage.  The target must make a DC 15 Con saving throw or become infected with the madness in the Death Burst trait.