>>102554255I think people forgot that the grass sword was a curse. Finn merely learned to accept it. All the time he had it he was giving it strength, the more he asked of it, the more it became a part of him.
And it did become a part of him...
Finns arm was replaced, courtesy of the grass sword. Its acted as Finns panic button or has reacted at times of high stress and emotional conflict. Hes been unconsciously feeding it strength, you can notice it get progressively more powerful throughout the series, it had to be drawing more strength from some where. Finn's been through a lot too, both this and the emotional stress would feed into a curse, so much so that it would be able to take a variety of not only physical forms, but non physical ones too. It gained enough power from Finn that it manifested itself into a demon later on, but ill get back to that.
Then prismo happened. In a plan to save himself from oblivion, he sacrificed two of his friends to time paradox. Finn would have absolutely ceased to exist, but he at that point was practically merged with the sword. So when finn touched his alternate self, he only destroyed his form. Finn had become a living blade, but bare in mind that this blade still had the curse.
Then he fucking loses it. The blade is then used by a bandit to loot and pillage. after the battle, finn sword was destroyed. But,when the grass blade ran through the Finn sword, it left a piece of itself with it.
The Finn sword is left in distraught in despair in a broken state, and keep in mind this Finn had a completely different life then Finn now unable to interact with anyone, this Finn as isolated and wouldn't have had anyone to support him anymore. He became an entirely different Finn time he was stolen. Alone he sat until the grass demon reveals itself. Its able to harness all of his negative emotions and posses Finns soul after he escapes with it.
Now it slowly corrupts Finn sword Finn, until it kills its original master.
