That was the episode "Upgrade" where Blakk was captured and brought to Stalagmite 17. "Back to Blakk" is where we got a glimpse of how Dr. Blakk became his vile, twisted, and pale self. Spoiler *Burpy was one of Dr. Blakk's slugs before he went over to join with Will Shane. My sister guessed that Dr. Blakk might've won him when he beat Jimmo Shane in a duel.* It's also the episode where Eli finally learns the truth about what happened to his dad five years before he came down to Slug Terra. Eli actually took the news better than I thought he would. He only demanded to know where Blakk sent his father and called him "Beyond Twisted."