I just found a pretty minor glitch on the Spirit Train stage.
1. Go to training mode.
2. Pick any character (I did it with Pikachu).
3. Pick Spirit Train.
4. Spawn a Warp Star on the leftmost part of the train (above Alfonzo/Toon Link).
5. Push it to the left by slowly walking into it. The Warp Star should stop rotating. It will never despawn, unless it is used.
EDIT: Also, if you spawn several Warp Stars in that exact glitch spot on top of each other, the glow around it will be brighter.