The Adventures of Superboy (1988) 3x5

An anonymous letter leads Superboy to Darla's hideout, where she has Lana locked in a meatlocker. She's holding Lana to blackmail Superboy, so he'll bring Luthor back through a portal (created by Dr. Winger) that took him to an alternate world. This alternate world is dark, and chaos has erupted as a result of Luthor's murder by an alternate Superboy. As Superboy tries to return Luthor, he and an alternate Dr. Winger attack him with kryptonite.