That's probably a crazy idea (because it would require a crazy amount of effort because of custoom chars and stages), but I always thought of something related to the Elder Scrolls series. Especially since after I found, downloaded (and lost) several stages that were animated screenshots from Skyrim.

Characters:
- Nerevarin (of course with Sunder and Keening)
- Vivec (magic type of character)
- Steam Centurion/Centurion Sphere
- Baurus (or any of the Blades)
- Mythic Dawn Agent
- Hircine
- Dovahkiin (with some Dragon Shouts)
- Almalexia
- Dremora
- Ordinator (Intro or taunt - We are watching you, scum!)

Minigames:
- Wave of Mythic Dawn agents, or Falmers
- Punch the Adoring Fan

Stages:
- Vivec cantons
- Dwemer ruins
- Imperial City
- Throat of the World
And more of all categories. Gosh, I would probably pay for it (not really)