Here is a list of ideas for characters for use in the storys or your own stories. They are all different versions of marvel characters, some are fusions and some are just different.
Groot + Hulk: A insane Bruce Banner caused by an accident with gamma radiation, discovers a strange sapling. After Banner uses the saplings power to break into his old lab then goes into a pit of gamma radiation with Groot causing them to fuse and having a Hulk/Banner relationship. While Groot absorbs most of the radiation from Bruce, curing his insanity except for random fits of randomness, Groot becomes highly insane(Not evil or angry or anything just extremely unpredictable and strange) and led by Bruces mind. Bruce can change back and forth on will but will sometimes turn during his insane moments. Groot is the same other glowing green eyes and at wounds, he can also shoot out green sludge that turns most thing it touches into wood(Think petrifying) and can control living beings that he petrified although some people can break out of the wood. The sludge also comes out of any wounds making unwanted wood piles in battle.
Vision + Captain America: Captain Americas body is found in the ice but not by the Avengers. After the Avengers defeated Ultron, his mind stone flew off into the sky towards the arctic, and broke through the ice and rested in Steve Rogers head giving him the power of the Vision.
Iron Man + The Destroyer(Asgardian armor): While exploring anciet nordic ruins in search of a strange suit of armor, Tony Stark(Pre-Iron Man) was among the explorers. While most of the party wanted to put it in a museum Stark wanted to study it, but when they found it Tony decided to get inside of it since it was opened up, then the armor closed up trapping him inside forever.