Tip: Make sure that ALL exit-enabled pipes, doors, etc. have a screen exit defined, or they'll take you to Level 0, the "endless" bonus game. Unless Start+Select is enabled, the only way out of it is to reset the game.
A rock which will fall at a random speed and will randomly be 16x16 or 24x24. Depending on the extra bit, it will either shatter or explode. Recommended for use with a sprite spawning generator. Requested by Aqualakitu and some others from #smwc.
If you uncheck "Don't use default interaction with Mario" with the CFG Editor, the rock will hurt Mario.