You mean, great partner for him in 2v2, 3v3, and 4v4?
Ganondorf is a great partner. He may run like a turtle, but he hits like a bulldozer. Mainly, you focus on racking up damage with Luigi's quite strong damage output and amazing combos, and leave it to Ganon to finish 'em off.
Bowser is also good. He packs a punch, just like Ganon, and actually faster than Luigi. Reason is up there.
And.... dunno for the others. Mainly, you want them to cover your weaknesses, but if they also help out greatly in one of your pros, then they'll be great too. Like Ganon, he is slower than Luigi, so he doesn't cover your mobility problems, but he helps out greatly on getting kills, since Luigi's range isn't very great and sometimes, he struggles on getting a KO. But Luigi racks up damage to the point that your opponent is all bruised there and there, and Ganon's kill power is probably the best in the game.
Though, I myself is not very familiar with Team Battles, so other Luigi mains may be able to help you out further.
