Divekick

Game still works perfectly online but it's kinda old at this point in the way it handles fullscreen and multiple monitors. With how sparse the playerbase has gotten you are going to have to get friends into the game to get the multiplayer achievements. You're going to want to set the region to "Global" for your whole group. This is a fighting game with two buttons (P and K) and no directional inputs whatsoever. You retreat by pressing K while grounded and most characters go in by pressing P -> K. Double dives muck it up a bit. Specials generally require meter ("kick factor"), are P+K and each character has two. You get the idea. Oh and it's balanced. There's a universally-agreed-upon best character but she's not oppressive enough to ban. The game is balanced around the fundamentals-oriented character Dive, who sports an even matchup spread with everyone else. Historically this is one of the first fighting games to have rollback netcode, beaten out by the Street Fighter re-releases and Skullgirls. Almost everything in the game is an unsubtle parody of something that was culturally relevant to fighting games in 2013. Most of it still is.

Divekick is the purest form of fighting games. Add to that some excellent humor, and you get a very easy title to recommend!