Just read this in some replys as a side node and liked it instantly.
Reverse Wave Battles against Galactus
Which means, you choose 3x3 teams and send them into battle against galactus, everytime one group is defeated next combo pops in to continue the fight!
This would be a lot of comic style were all heroes and villains fight to gather to save earth, you can send in your best avengers, x-men, hero for hire, whatever team in to fight against mighty galactus.
For example, the mechanic can maybe like this, you give him 100k infighting health and let your alliance fight him down as usual. Counterside at the end of one fight you may have 9 (if you have a deep roster with 2s, 3s and/or 4*s you should go a couple of rounds before your complete roster is defeated) knocked down characters, but a lot more playtime against galactus.
And in the end Silver Surfer pops up and saves the day (^_^)