You first need to unlock Loki. This can be done in single player. Then take the two players; make one of them should be Loki, switch to the other one (triangle) and make him Hulk.
The player should use Hulk and attack Loki with square over and over. When Loki dies sometimes hulk will do the special move (from the Avenger's movie) and smash Loki around.
While I was trying Hulk did a special move on Loki at one point but not THAT special move. The trophy only unlocks on that specific move from the avengers movie below. This trophy should only take you a few attempts after you unlocked Loki.
Note: Marvel owns the avengers and pretty much everything else related to this clip....