Antasma

Antasma is the supposed primary antagonist in the upcoming game Mario & Luigi: Dream Team. It is a being who destroyed the Darkstone in order to create chunks that froze the Pi'illows. Mario and Luigi are tasked with rescuing the Pi'illows which Antasma froze. It's appearance gives the impression of it as a knightmare whichthe Pi'llows fear.

Trivia

 * Antasma seems to bear similarities in appearance to all of the previous final bosses in the Mario and Luigi series. (Cackletta, Elder Princess Shroob, and the Dark Star.)
 * Antasma's name is likely derived from the Latin word phantasma, meaning "spectre" or "apparition."