All you have to do is turn on a second controller and, when pressing start to select a character, choose Arcade mood instead of Coop. Play any level, and get more points than the second player. If you're playing alone, then it is impossible not to win, as the second controller only does things if you tell it to. If playing online with a friend, you can ask that friend to let you win one level. If you're friend won't let you win, you'll just have to try your luck. Kill lots of enemies, collect health/mana orbs, grab S.H.I.E.L.D. coins, etc. You only need one win, so it should come fairly fast.