Finding White Mushroom Houses:

If you have enough coins in certain Levels you¹ll find a White Mushroom
House back on the map.

The minimum amount of coins needed at the different levels are:

World 1, Level 4 -- 44 coins
World 2, Level 2 -- 30 coins
World 3, Level 8 -- 42 coins
World 4, Level 2 -- 22 coins
World 5, Level 5 -- 28 coins
World 6, Level 7 -- 78 coins
World 7, Level 2 -- 42 coins

The White Mushroom Houses in Worlds 1, 3, 5, and 7 wil give you P Wings. The
White Mushroom Houses in Worlds 2, 4, and 6 will give you Anchors.

No More Dry Bones:
Dry Bones will disappear if you make him into a pile of bones and then walk
across the screen until you can no longer see him. When you go back he will
be gone.