Corrupted Entity

Amorphous. The Corrupted Entity can move through a space as narrow as 1 inch wide without squeezing.

Spider Climb. The Corrupted Entity can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Tendril Grasp. The Corrupted Entity extends a tendril towards a creature within 10 feet of it. The target must succeed on a DC 12 Dexterity saving throw or be grappled by the tendril. While grappled, the target is restrained, and the Corrupted Entity can use its bonus action on subsequent turns to continue grappling the target.

Self-Explosion. As a desperate measure, the Corrupted Entity can choose to unleash a devastating self-explosion. When it does, every creature within a 10-foot radius of the Corrupted Entity must make a DC 12 Dexterity saving throw. On a failed save, a creature takes 4d6 piercing damage and is knocked prone. On a successful save, the creature takes half damage and isn't knocked prone. After using this ability, the Corrupted Entity is destroyed, leaving behind only remnants of its dark essence.

Corrupted Influence. The Corrupted Entity attempts to bond with a creature it has grappled. The target must make a DC 12 Wisdom saving throw. On a failed save, the target is possessed by the Corrupted Entity. The Corrupted Entity gains control of the target's body, and the target is incapacitated. The Corrupted Entity has access to the target's actions, and adds +2 AC to the target creature. The target can repeat the saving throw at the end of each of its turns, ending the possession on a success.