Trickster

Tricksters are hostile mobs that spawn in the Underground of the Overworld. It is a melee mob which creates a clone of itself every 8 seconds. Before creating a clone Trickster will turn invisible for 3 seconds, and then a clone will appear next to him. Upon the creation of a clone the Trickster will laugh. When a clone is killed it will explode. Trickster's clones only have Heart.pngx15. The Trickster will only spawn below Y = 25. The Trickster has the Attribute of Explosion Immunity, however its clones do not.

References/Sources
http://adventofascension.gamepedia.com/Trickster