Warlords

You can easily do this by yourself, I just did it, and I just started playing this game.

When you start an Evolved game, have two controllers ready. The second controller doesn't need to be signed in. On the start screen, press A on both controllers, and you are in a Local 2-Player game.

What you want to do is move your second player to the middle (the apex?) of your wall, so it is at least defending some balls headed his way. This should be enough. For now, focus on Player 1.

With Player 1, attempt to catch a ball by holding A. Once you have a ball, move your paddle all the way to the highest point possible, so you're facing the green base. Release A when the AI is not defending there, and immediately hold A again, so you should catch the ball again on the rebound. Sometimes the AI will be defending that upper corner, in that case either wiggle a bit to try and pass it anyway, or shoot the ball in another direction and try later. It should take about three to five shots to expose his king and destroy him. Once done with that, move Player 1 to the middle of his base (or any hole that might expose your king), and change to Player 2.

The same tactic applies for Player 2, but you want to move to the lowest point of your and the yellow AI's base. Once you destroyed both bases using this cheap way, you can destroy one of the player bases and king, and you advance to the next wave. I easily reached wave 6 using this method, but the achievement pops at the start of Wave 5. Good luck!