1x15 - ThunderCats Roar

Lion-O never pays attention during Tygra's training sessions so when he's asked to do a pop quiz on "sword magic" he accidentally opens a portal to the Astral Plane and releases the Nether Witch. The Witch imprisons Lion-O and Tygra in her nightmare realm and it's gonna take a lot of studying to figure out a way home. Wonder if the Astral Plane has any great teachers lying around.