FINAL UPDATES: AT SEASON PREMIERE

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Hey everyone! I'm here with the FINAL update for the Adventure Time season premiere! The picture above is from footage that was released from the new episode. Farmworld Finn and Jake are in a cave being held up by an old lady, who appears to be Marceline, by the looks of her boots, with a laser gun. Next to them, is this, Simon Petrikov crushed under a giant frozen warhead. The "Marceline" tries to shoot Finn and the laser just goes through him without affecting him. She then yells at the gun and Finn takes Simon's crown and walks off and says he has to save his dad, who is being attacked by The Destiny Gang.She yells in return, "Yeah, more like destroy the world!" She is also referred to as "The 1000 year old lady" so it is definitely Marceline, judging also by the fact that she is guarding Simon's body. 

Here is the footage

There's also an animatic for a part of this episode where Finn's mom, Finn's dad, and The Destiny Gang are shown. Finn's mom is holding a baby, and his dad is getting pushed around by The Destiny Gang. Finn's mom tells him to sell Bartram, the family mule, for all the money he can get. Finn then says he loves the mule. They then turn and see Finn's dad getting pushed around, Finn's mom says that everything will be okay, and to do as she says.

Animatic