The potion is a green chemical and is in a conical flask.
Role in the episode
As its name implies, it causes permanent paralysis in any living being. Finn and Jake decide to spray the potion on some imperfect tarts after stuffing them into an anti-gravity tote chamber. They then carry the tainted tarts by accident, serving the original purpose Finn intended: to paralyze potential tart thieves. In the end, the paralysis takes effect, as the Butterfly With Laser Gun is seen drifting away motionless after eating a tainted tart. It is likely that Grimby and Taddle were also paralyzed.