You are free to use my ideas from the fanfictions I have made if you wish:
-The Disney characters are being pulled into another dimension mysteriously known as Infinity.
-Nobody knows quite why they were chosen, or why their worlds were chosen, and the plot is to find out why they are there and to find their way back to their worlds.
-The sub-plot is that the villains have also been brought to Infinity. They form an alliance together eventually, after much fighting against each other.
-Mickey is the leader of the kingdom of the Disney Heros, secretly in search of his magic hat to possibly conjure everyone back.
- When Marvel comes, people begin to take sides whether or not these dangerous heros are who they say they are.
-In one chapter, Green Goblin has captured venom an infects most of the DIsney characters and Marvel alike. Much like the playset. I made concept art for Rapunzel with Venom and she looks terrifying with her hair.
**SPOILERS** (If he actually used these ideas)
-To get back home, Mickey and friends are urgent to build a portal with the help of Phineas and Ferb.
-However, if even one character returns home, all of the characters do. This causes the taking of sides amongst hero and villain. Who wants to go home and who wants to stay.
-Eventually a civil war starts between the characters, the fight to stay or go home. Villains sided with heroes, heroes sided with villains. It'd be epic.
-Eventually you find out the magic sorcerer (Sorcerer's Apprentice short) has collected everyone from different dimensions to make the Ultimate team. Hero and Villain must once again side together, this time all as one, to fight a greater evil and return home.
Feel free to add on, give or take, or not use these ideas at all. Just brainstorming.