Cassiopeian Dream Eater

The Cassiopeian Dream Eater is an alien organism that attaches itself to the face of its host, then feeds of the chemicals produced by the brain during stress by trapping the host in a nightmare.

The Dream Eater has a very strong grip on its host, as mentioned by Kevin in Night of the Living Nightmare it would be impossible to remove it without ripping the victim's face off. Presumably it can be removed by a Galvan doctor.

A Dream Eater appeared in Night of the Living Nightmare, where Albedo attempted to use one on Ben to force him to remove the Ultimatrix. However, he slipped on a spilled smoothy in Ben's bedroom before he could get to Ben's bed causing him to drop the Dream Eater on himself. This resulted in him being trapped in a nightmare in which he succeeds in placing the Dream Eater on Ben and then tries to get Ben to remove the Ultimatrix by attacking him with his previous foes, as well as Julie, Kevin, and Gwen. He finally attacks Ben himself before being defeated by him followed by an attack led by an army of Ben's alien transformations.

Trivia

 * The Cassiopeian Dream Eater resembles the Rutan Host from Doctor Who.