The easiest way to earn this achievement, as well as many others, is to go to Vezok's deluge. once you start up the level, play until you go gold and then just keep defeating enemies. As long as you don't use your gold powers more than once or twice, the enemies will be set on infinite respawn. This helps with all of the "X amount of victories with (insert name)", "Defeat X amount of (Insert Enemy)", "Collect X amount of Lego pieces", and it also helps pay towards the upgrades and abilities (100% achievement).