Given the Mark vs. Supes thread - what about this multiverse wandering:

1. Viltrum empire - a few of them (let's say 5) try to take over Earths with OP magical types:

a. Anos Voldigoad and his buddies
b. Wang Ling, the Immortal king - any other typical OP Heroes you want to try out.
c. MU - opposition will be Classic Fate, or DC - Classic Fate - no Spectre (stomp)

2. Run into the GLC at the height of its staffing with the classic Guardians (probably a stomp) but you can bring in all of the Viltrum if you want.

3. The Culture Universe, the Galactic Patrol universe with both the Children of the Lens and all the Arisians in the game. plus the 2nd stage Lensmen and the millions of GP space battleships with their shields.