This is a disassembly of sprite A1 in SMW, the bowling ball-esque sprite that Bowser drops. I made it so that if the extra bit is clear, it acts exactly like the original, meaning that it checks for a specific Y position to determine when to start moving horizontally. If the extra bit is set, it actually detects ground.
NOTE: This sprite requires the No Sprite Tile Limits patch. It draws 12 tiles at once, which isn't a problem for "special" sprites in the original SMW, but for custom sprites, yeah, you'll need the patch.
Tester's note: If you (= the user), for some reason, don't seek to apply that patch, then sprite setting 12 also works.