I know this is probably going to get marked as spam because I've said it before, but this issue with Halo 2 Legendary co-op needs to be addressed. Please turn of the Iron skull effect for Halo 2 Legendary co-op. You say "that's the way it's always been", but that's not an excuse. It's not fair to gamers when their partner makes a mistake in the campaign and both players have to suffer by going back to the last checkpoint. It nearly makes co-op unplayable, because there is always the possibility of you or the other player picking up slack. It also doesn't make any sense, because there's already a skull that does that. I'm hoping you don't just leave this co-op in an unfinished state and really consider what I'm saying.
Sorry, but this is how original Halo 2 was as well, even before people knew of these skulls. Sure it's a pain, but look at it from this angle, if you played solo and died what happens? Last checkpoint correct? So you have twice the fire power in coop, should be less mistakes, it plays no different than solo rules, you just have more ammo. Either pick your partner more carefully, or like most others you will start to learn the levels, where possible enemies spawn. You end up a better player in the long run. With that being said, go for par score and turn Iron skull on for multiplier, its already on anyway for coop, so get extra points from its redundancy.