The Crystal Mergence of Destruction is a sandwich that when licked, can suck people into it.
The sandwich used to belong to a Military Dog Force in the Crystal Dimension, but Lee stole it. Lady Rainicorn being his accomplice, stabbed him in the back and fled to Ooo where she hid it until, in the episode "Lady Rainicorn of the Crystal Dimension", T.V. snooped around the kitchen, found it in a secret hiding place and ate it.
Lee tracked it down and made T.V. believe they were friends and made him spit out the sandwich to keep it for himself. Once he licked it, he got sucked into it and disappeared. Lady and T.V. put it back in a box in the secret hiding place, keeping it safe.