Tip: If you give a Muncher tile custom graphics, it will still act like a coin when a silver P-switch is active, whether it looks like a coin or not. So make sure to use ExAnimation if there's a silver P-switch in the area.
These are blocks that resemble the P-Switch from Super Mario Bros. 3. pswitch.asm and upsidedownpswitch.asm are the actual P-Switches, pswitchquestion.asm is a block that spawns one of these two blocks. You have to adjust the Map16 number in the .asm file. Various other things can be changed too.