You have to turn your character clear as well as remove your hat and cape to count as invisible. That may make this task seem impossible, but there is a trick. Make one run to level 25 in Escalation normally (with your normal character) to unlock the jetpack version. Then start again with the jetpack and turn yourself invisible like described above. You'll notice that, while YOU are invisible, you can still see your jetpack! Get through 20 levels like that, and the trophy is still yours!