To obtain this achievement you need to send 10 maximum difficulty waves to your opponent in a versus match. As the only multiplayer available is local splitscreen, you will have to either do it by yourself with two contollers (Which will simply require you to play a few games) or convince your sibling/spouse/neighbour to help you out to do it in one.
First, I will detail a little bit what "difficulty waves" are. To send waves to your partner, you need to perform combos. The higher the combo, the more difficult the wave you will send. After you have finished your combo, you will see a symbol of a worker move over to your partners side of the screen with a multiplyer number next to it. If it says 'x24' next to it, you have sent a maximum wave. The combo you will need to send changes as the game goes on, so there is no set number I can give you. For the powers, use Earth and avoid Water. You can use your own preference for Wind and Fire as they are similar.
Now load up the first temple in a competitive match. If you are going up against someone else, you will most likely both naturally get the achievement just by trying to get combos. If you are going up against yourself (Meaning the controller sitting alone next to you), then you will have to do a few games. Don't worry though as it typically only takes 3 matches to complete at a few minutes each.
NOTE: If you are doing this with an idle controller, make sure you restart at the end of the game. Do not leave the 'game session' by going back to the menus as it will wipe your current tally. Thank sirbradenwalker for figuring this out!
Achievement unlocks as soon as you send the last wave :)