These blocks have unique gimmick when mario is sliding, these include:
-a "ramp" (actually the custom block is being place above it) from SMB3 that if Mario gain momentum from sliding downwards and press jump when hitting the ramp, will make Mario do a long jump, the arrow gfx for that is optional, you can use a blank tile.
-a solid block that can break if Mario slides into them.
-a "continue slider" that keeps mario sliding indefinitely if he prior slides into them, the modifyable speeds are the "minimal" speeds that moves mario if slower.
-a passable bridge that is only solid when mario is sliding on it (without falling onto it)
-and much more..
These are useful for puzzle and slide based levels.