Originally Posted by BigMaki
Enemies in sections will only respawn once you've gone to a different act. So extract to any extraction point in any other act, then extract yourself back to act 1 and they will be there. Repeat this as many times as you need to...
You don't even need to be online to get the 4-player achievement. It can all be done on one system, provided you have 4 controllers. All that matters is that each character is controlled by a separate controller. If you and your friend each run the game controlling 2 characters with 2 separate controllers it should unlock. The quickest way to do it is to go back and forth from Tony Stark's Lab to Stark Industries in act one 25 times.
I'm trying to do the Arcade wins and I haven't been able to get the enemies to respawn. I've even tried extracting to another act, but they still don't respawn.
Is there any other advice that can be given?