Gate Guardian

the gate gardian apeares in the epiosode death in bloom in wich it dosen't let Finn and jake in since they are alive however they destratct him long enough and walk in the gate behind him he then yells for them to come back but they were all ready to far gone to care.The gate gardian apeares to look like a skeleton bird with one large eye.

Trivia
The gate guardian may be baste off of cerberas a three headed dog that guards the gates of hades.