Crumbling tiles first appeared in Run 3. They have a grey texture with cracks on them. They are a pretty common tile, as they are sprinkled throughout the various levels in both Explore Mode and Infinite Mode. The first level that features them in it is Level 3.
In Level 3, you see some gray tiles with cracks. Those are crumbling tiles. You find out that unlike normal tiles, they fall when you step on them! You can think of them as a "Step on it and it replaces with a Hole" tile. Also, if you step on one that's in a group of crumbling tiles, the entire chain starts to crumble. This is implemented a lot in levels like Level 10.
If you use the Child, due to him being lightweight and his balloon, he can walk on crumbling tiles without crumbling them. They only crumble if he jumps on them. So, in Level 10, where it is made up of normal tiles and crumbling tiles entirely, he can win even if you leave it alone. That is why the Child is best when a level has a large quantity of crumbling tiles.
With careful timing, you can still walk on and jump off of crumbling tiles that have already fallen.
- Player 03 once revealed that Crumbling tiles were originally Normal tiles, but suffered against physical damage (coming from unknown sources). That is why they cracked and will crumble so easily.
- In the Infinite mode trivia, the Child called them gray squares. This shows the Child's age.