Smashboards

Should Rhythm Heaven be in distinct, not Mario or Non-distinct part of distinct? (because of crossing over with WarioWare)
Edit: How about Wario's Woods or the Donkey Kong Country cartoon? (is the latter part of the same DKC games)

Rhythm Heaven isn't suddenly Mario because it has a few crossovers, is Zelda Mario in that case?

Rhythm Heaven: Not Mario (for now... could change in future depending on Groove and future WarioWares)
DKC cartoon: Non-distinct
Wario's Woods: This one is actually really weird. Distinct if SMB2 is just part of regular Mario, non-distinct if SMB2 is it's own series. Like it's right in that uncanny valley of being removed from everything else, but having enough SMB2 content to prop it up just barely.

Why is Luigi’s Mansion less distinct than something like Yoshi’s Island?

Honestly, I think the thing about Luigi's Mansion is kinda that well... Mario is there, as an adult, in the plumber outfit. Does that make sense? It's probably contradictory, certainly superficial, but I just can't bring myself to see Luigi's Mansion as fully distinct simply on virtue of the hero character dynamics and designs not being particularly different. While they also could count under the same logic as Mansion, Mario Paint barely has Mario in it and Mario Kart has so much well-known but exclusive iconography (Rainbow Road, blue shells) that I have to give it some distinction - and Mario Strikers (at least early on) very clearly doesn't take place in the conventional Mario world, while Luigi's Mansion more reads like a different side of the same universe,.

If the Mario rpg games are fully part of mario, SMB2USA outta be too, the vast majority of them are about Mario character visiting strange lands never seen before or after, much like Mario 2

I suppose there's an argument that the circumstances of SMB2/USA's development lend to it being a spinoff, given it was converted from a promotional game for the Yume Kōjō festival... and, by that logic, one could argue the "true sequel" to SMB would be Lost Levels. That said, I'd argue its still applicable for mainline classification just based on intention, given its reworked US release was intended specifically to be in the SMB series. (And, fun fact, the horizontal scrolling was added as part of a request for the game to be more "Mario-like", which doesn't actually play into my decision, but I think is a neat tidbit regardless.)

SML on the other hand? I'd argue it leans more on the side of being a seperate series despite similarities to mainline SMB in terms of gameplay, more as a branding thing. (And it helps that the games in that series have a distinct setting to SMB, not to mention the later Wario-led titles.) Though... I guess that brings up a question of whether Wario Land and Mario Land are the same series too, which is a whole other can of worms...