Cranial Encyster

Disquieting. Any creature who starts it's turn within 30 ft. of an Encyster must make a DC 13 WIS save. On a fail, the targets are stunned. They can make the save again at the end of each turn. Whether a creature makes the save or not, it is immune to the effect for 24 hours after.

Attach. When the Encyster makes a melee attack against a stunned opponent, it can attach itself to the target. When it does this, the target immediately loses the stunned condition. A creature with whom the Encyster is attached to can attempt to break free from the monster with a contested Str Check, at disadvantage, on their turn.

Death Urge. On the next turn, after being attached, an effected creature must make a DC 16 WIS saving throw. On a fail, they fall unconscious. On a save, they can remake the Str Check at the end of their turn.

When an unconscious creature creature starts its turn. It if afflicted with a Death Urge. The creature must use all available actions, including multiple attacks, to inflict self harm. If the target is wielding a weapon, they automatically succeed on an attack against themselves. If unarmed, they will move toward an enemy and provoke an opportunity attack. If there is a potentially harmful environmental hazard, they will willingly move to it (i.e. a bonfire, cliff, or dungeon trap). If there are no options, they do nothing. 

Tentacle Attack. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 7 (1d6 + 4) piercing damage.