Warhammer 40k: Space Marine
That would be cheating in multiplayer, as co-op is tied to competitive progression.
It's still cheating in multiplayer - Exterminatus has scoreboards (that are always on, regardless of whether the party was private or not) and still gives you basic XP.
Well, I consider it to be, anyway. And you run the risk of getting banned and such, so I think it'd probably be better just to say:
No, the trainer is not meant for anything but the campaign.
[Edited by Shotgunmaniac, 12/22/2011 8:38:57 PM]