You really have to get ridiculously lucky, because the AI all got fluff for brains now. I lost interest in Arcade mode when the update to dumbify the AI was released. On the normal levels, there's no challenge, and on the levels like the one you are describing, they don't try to fight you so there's no way to kill enough of them in the time provided. It was not a useful update in any way. Was anybody really asking that EA do this? Maybe a few whiners, but not normal players, that's for sure.
I'm at 45 of 48 and stopped trying to finish off the last three tier 3 challenges since it's just a waste of time and effort. Just to prove how useless the AI in Arcade mode is, I made a video where I run right into a crowd of troopers and after I kill one of them, the other four run away and the rest of the troopers on the board disappear. Now how am I supposed to kill 40 troopers in three seconds when they act like that?
