If you really wanted to get crazy you could make "boss" include all stars held by NPCs where interaction with the NPC is required to get the star. Would add both Koopa races, Lil Penguin Lost, CCM slide race, Can Eel Come Out to Play, Manta, THI Piranha Plants, monkey cage, and maybe some more I'm missing.

Does Unagi in JRB count as a boss?

I've thought about this as well, but not sure which mechanics are glitches. I think bomb clips (e.g., pless) are glitches, but I'm not so sure about things like triple jumps not being affected by slopes or the fact that HMC has no ceiling. Would cannonless be banned?