The Cursed Jello

“Jack? Jack, wake up!” Shouted Marlene as she entered his room. Jack and her had moved in together just weeks before. She knew his Spello Jello addiction would cause him some trouble. He was having at least five bowls a day. She went back into his room with his water and saw that he was vibrating rapidly.
She dropped his water on the floor and, as she came back up she noticed that he had stopped shaking. She went over and looked at him. The words “Are you alright?” had barely left her mouth when his eyes snapped open. They were solid black.
He pounced on to her and when she cried out he stopped, his eyes reverted back to their normal green. He showed obvious difficulty taking control when he said “Can’t... control... jello... cursed... RUN!”
She ran as fast as she could as he thrashed around on the floor, obviously fighting with his own head to take control. She crashed through the front door and bolted it shut as fast as she could.
As she tumbled her way down the hill she heard Jack, well, he used to be Jack, thrashing against the door attempting to knock it down. Eventually, she managed to reach the nearest doctor. She described the situation to him and he immediately came running with his medical kit.
They got back to the house and found the door unbarred, dwindling on its hinges from the brute force that had knocked it open.
And Jack? He was gone. Gone. Forever.