The Amphibian Man is from the 2017 Guillermo del Toro movie The Shape of Water.
The Amphibian Man is seen very briefly hiding in the floorboards under Lisa Simpson's bedroom. He is holding an Oscar trophy in his hand, which represents the award the movie had won. This is also a long running gag in the show where the audience sees strange oddities hidden in the foundation of the Simpson's house.
Amphibian Man was in the same tank as Kang in Treehouse of Horror XXX. Kang called him a freak then started to cook him. Selma told him to turn himself as she and Kang were going to make out and the Amphibian Man asked them to kill him now.