Tip: Switch palace switches normally disappear if you replay the level. However, if you insert them as direct Map16 and use the hex-edit at $00EEB2 in the ROM map, you can replay the level without a problem.
This is the infamous "Ultimate Noob Boss" made by Iceguy/Nesquik Bunny. It is now back with a new name that implies it can be used for more than boss fights. It has quite a few attacks and is very customizable. Read the comments in the .asm file for details.