Rigby's Bodiless Consciousness was the result of eating way too much junk food. In the episode "Rigby's Body", the Bodybuilder's bodiless consciousness took Rigby's body and dressed it in strechy clothing after Rigby was thrown out of it.
Rigby's consciousness is a green blob. It has tiny limbs which act like arms. It's eyes are the same as Rigby's with the dark circles around them.