Ghostbusters: Spirits Unleashed Ecto Edition

I found this easiest to do on the Museum level with the Wraith. I played with bots and picked out one of their names that would be the easiest to remember. I targeted "Hotshot" as soon as the game started. I used the special "Y" ability that the Wraith has and Slimed him once. I then ran to recharge my energy. I stalked him a little bit until he was only near one other Buster. I used the Wraith's Unique ability next to stun the Buster then I slashed at him with the RT. I then just repeated the same process until I got it. If you're going for just this Achievement in a bot lobby you should be able to get it with little to no difficulty.