Mario's slightly Unusual Boss Rush is a SMB3-inspired fangame where Mario goes around defeating bosses in levels based on franchises that are not his own.

Mario is invited to Peach's Castle for a grand celebration of some sorts. When he has almost arrived, Kamek appears out of nowhere and zaps him far away. Now Mario has to make his way back while going through some unusual worlds with folks who seem to have a bone to pick with him.