[s2e26] Heat Signature [UPDATED]

In the episode itself, Marceline convinces Finn and Jake that her ghost friends can turn them into vampires so they can survive a trip to a "ghost dimension" to watch the movie. However, it turns out to be a played by Marceline and her ghost friends, who lead the duo through a series of "vampire" tests that are actually just dangerous stunts.

It follows a submarine crew that detects a "heat signature" from an enemy, only to realize they cannot find their own signature, suggesting they might be ghosts or in a supernatural situation. [S2E26] Heat Signature

The film's tagline is "Under the ocean, no one will hear your death" —a play on the famous Alien tagline. In the episode itself, Marceline convinces Finn and