The Possessed

The Possessed is an enemy from the Solar Eclipse event. Despite not resembling one, it acts similarly to spider enemies such as Wall Creepers, Blood Crawlers, Black Recluses, and Jungle Creepers, climbing on background walls when able to and walking on the ground at all other times. While climbing on walls, The Possessed seems to have an increased movement speed, similar to the other enemies that share this wall-climbing trait, and a 100% resistance to knockback.

Trivia

 * The Possessed is a reference to the 1973 American supernatural horror movie The Exorcist.