What annoys me about XBOX Live is that you cannot send games to people. I'm getting my brother an XBOX One for Christmas, and I want to send him Killer Instinct Ultimate. We used to play the original game a lot, and I think it'd be more fun to have it included than to just get the Combo Breaker pack, which has a physical release.
To be fair, PSN doesn't support this either.
I haven't tried it, but what more do you need than just two people in the same area? That's pretty much how it works in Resogun, but to be honest, I don't really like it much. It's harder to play because you don't stay in the middle of the screen at all times and one player can drag the other around with a boost. Essentially, it's just really hard to go from complete control to shared control like that... especially in a game where finite controls are imperative to good gameplay.
it's clearly tacked on for the multi on gw3.
2 people would be fine, if it wasn't geared towards 2 teams of 4. and it has 2 modes - get high score, or who beats the boss first.
the boss mode you have limited ammo, 50 max, and it's shared on the whole team. they have ammo things you pick up on the map. but 1 on 1 is stupid. you face a separate enemy than your opponent too. all you see is your opponent's icon flying around - you dont see any bullets, or any enemies that they see.
then in the "high score" mode, it's the same - you can only see the opponent, not the enemies they are shooting at or the bullets they fire. you don't even fire at the same enemies that they fire at. and it's like a king of the hill type of game. there are 2 "posts" that disperse enemies for whatever team "owns" that pole. you "own" it by shooting it until it is yours. then the opponent can take it back.
so when its 1v1, it's so dumb because there are 2 poles and you each basically have 1. and the enemies that come out are the basic ones, you can basically circle the pole and not worry about anything. it's just a dumb online mode.
and i'm not sure what you mean about KI. they have multiple versions. the combo breaker version you can buy online too, it's the $20 version. the ultra one is the $40 one. i'm not sure what the ultimate version is though.