i've been trying to get this powerup for days and i can't seem to unlock it, i've levelled up from lvl 54 to lvl 80 in this level to unlock the ultimate deadly attack but no matter what i do i can't unlock it, i've spent 15-20 mins each time but it doesn't work, anyone that's got it wanna give me some tips on how to get it?! it's really starting to p*** me off now!