Really simple achievement so long as you can remember which character Dweezil is. Luckily, a hint pops up on screen as to when you can knock Dweezil over and bounce off of his belly. In Level 1:1, Dweezil can be found to the left lower part of the level. Knock him over using

or jump on his head, and then simply jump off his belly for an easy 5g.