Tip: If you place a moon, midpoint, or dragon coin through Map16, it will always respawn whenever you reenter that sublevel. It will not respawn if you add it through the Add Objects/Extended Objects window.
This is an horizontal version of the Layer 2 smasher you see in, for example, Wendy's castle.
Altough it may seem confusing at first, it's very customizable after you understand how it works. Be sure to read both the asm file and the enclosed readme to know how to configure this; I also included an example level so you know how to configure it.