Why limit yourself to only a level or a custom boss? You should make a level that ends in a custom boss fight; too many stage bosses are just either one of SMBX's pre-programmed AIs or a sprite swap of said AIs.
Jacob9300Shadow wrote:Why not make a survival level? If yiu need more info PM me.
Survival levels usually start out well during the design stage but they usually descend into some insanely-difficult Touhou level with no room to dodge projectiles.