Though the game prevents you from throwing Mushroom Blocks when you're in front of certain background objects, it's possible to stick a Mushroom Block inside or next to the background object, as long as there is empty space around it. These objects include vines, ladders, chains, doors, girder platforms (World 3-3), waterfalls (5-1), trees (5-3), and sand platforms (6-1).

While you're moving towards the empty background, throw the Mushroom Block when the front of it is lined up with the edge of the background object. Once it's stuck in the background, the Mushroom Block will change color to match the sprite it replaced. If you pick up the stuck block, it will leave a square hole in the background, and the Mushroom Block will change back to its normal colors. Using the same technique, you can also throw Mushroom Blocks into solid walls that are touching the top of the background objects, such as the rock wall above the sand platforms in Birdo's room in World 6-1.

To get the Mushroom Block to float next to the background object, move towards the empty background, then throw the Mushroom Block when about half of it is outside of the background object.

When your character is small, you can stick a Mushroom Block in the top half of any door (except potion doors) that has space around it. The door will still work, even with the block in it!

Bonus glitch: You can throw another Mushroom Block into the same spot occupied by a stuck Mushroom Block; the one you threw will replace the old one. See the disappearing Mushroom Blocks glitch for another variation.