Multiplayer Achievement Glitch
a few times while playing coop with 2 other people, the game would glitch and one player (me) would get locked behind a previous checkpoint wall. The other players were able to beat the level without me, and I got the achievement for all shoes in MP..
So I ultimately got the achievement for beating all MP levels with shoes, but didn't get the achievement for beating all MP levels.. (naturally impossible). The other players got both achievements.
Hope I don't have to do the entire MP again as it was quite hard.
I remember the level it happened on 3-14, so I'll give it another go and post back if it unlocks the achievement.