Playing alone

What can you play alone on Halo 3 and 4 besides Campaign mode?

Set up another controller and pretend you're a winner.

I think Spartan OPs from Halo 4 can be played solo

Forge

Did not really look at the time, but no offline skirmish mode?

You can run around in local MP and shoot the other non-playing person.

LMAO

Even on Easy mode you get swarmed alone. I like it because it can be tough.