For example: If you wish to make a goomba not able to be stomped, you would do the following. In the folder for the level you wish to use a custom NPC in, you will create a file with notepad (a program that comes with your computer) that is named the same exact as the graphic file of the NPC you wish to alter. All custom NPCs are set just like custom graphics and are done manually by the user creating a file in the game folders. It is not part of the actual programs user interface. fallingsnow Guide also featured in the SMBX Editor Help File -By Redigit and Blue While the feature is implemented in SMBx. It is also featured in the SMBX Editor Help File. This is from a forum thread at SMBX forums relating to custom NPCs.