Ok so to do this you need to play the Martian Fashion Show online with another player over Xbox Live. Once the level starts have one player pick up the yellow Ilidium bar straight ahead. Now have the same player collect the bars along the ledges towards the Cloning Chamber. Now once both players are inside the Chamber have the bar-collecting player collect the rest of the bars in this room (there is enough to make one full bar). Once done gather all of the green guys and gather them in the middle of the room with both players standing on top of one of the Cloning machines. Now have the player not collecting Bars jump down and do the X X X attack on the enemys and once one of them has the stars around their head, the Bar collecting player should jump down and use the A Y attack on the enemy with the stars. Note this will take maybe 3 attempts before any enemies will die just make sure they are grouped closely together. Now this took me and my friend a good few attempts to get a Combo of 9 but keep at it and you will eventually hit the 9 you need :D. Hope this helps.