As long as the infinite/100% combo's are avoidable and you can actually find weaknesses of the infinite combo, then it is legit, but if you got easy-to-do infinites like in MKD, then you are forced to play legit high level play (unless you want to play who does the infinite first

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This Ermac combo is legit because
1) Its not a 100%
2)You can not do it consistently like you can do inf combos in MKD
3)It's hard enough to not even effect the high level play of the game (You don't really see that many people doing 100% combo's off the bat do you?)