Near the end of section 2 I accidentally threw a Ball Rabbit on top of another ball rabbit and it flew off at near light speed and SMBX crashed with this message:
Also I'm just wondering, what's with Mario randomly teleporting left and right after you spinjump once? Is it to discourage the player from spinjumping? If so I feel like that could be explained better (or even implemented in a better way) because it took me several tries to realize spinjumping even caused it to happen in the first place. On a similar note it took me a long time to realize that the crows on the secret path were generated when the ball rabbit hit the edge of the screen.