Well, I definitely think that derivatives of actual characters (ex: naruto as a dog) should not be allwoed; those are copyrighted characters and to make money off them in any way (adoptables, commissioned art to draw naruto as a dog) is technically illegal because you're profiting off of someone else's IP). This should also include Pokemon, unfortunately, as well as Pokefusions and gijinkas. Fakemon are a bit more of a gray area, and I'd assume they're more like fan characters. Nintendo is very sue-happy when it comes to their IP and people profiting from their stuff,a nd it could get users in trouble.
+1 On banning Canon Characters being uploaded.
+1 On the canon characters as furries and/or feral animals being banned. Also includes recolors of canon characters (I'm looking at you, Pokemon fandom. just because you made your Pikachu pink or gave it spots doesn't mean it isn't still a copyrighted character).
As for characters inspired by the look of other characters (let's say for example, if someone was making adoptables that are the children of X character or even children of X character and Y character), I think it should be allowed since they may look like the parent character(s), but are not. A user can write that a "child of X canon character" has their own personality, maybe adopted quirks from the parent (ex: verbal quirks like maybe a saying, or sound added to the end of words), and maybe even a shared birth mark (ex: Fire Emblem Awakening's royal family has a special birth mark that is passed down from generation to generation to symbolize the child's royal blood)
-1 OCs in Canon Settings. Fan characters should be allowed. I agree that using uniforms may be seen as a gray area, however characters do also have casual clothes/civilian clothes, so it shouldn't be mandatory to have the character in a canon uniform all the time. In the sense of My Hero Academia, hero outfits apply as being something off-canon since it would be an original design for the character.
+1 to ban OCs of a canon species. I am a bit tentative on this, but I am mostly expressing this with Pokemon, because again, NIntendo is very sue-happy about their IP being used for profit in ANY form. It violates copyright laws and technically, profiting from drawing canon characters (via commissions or e-sales of fan content like stickers or prints) for most franchises I believe is also a copyright violation. Flight Rising IMO is a gray area since dragons can be different, and the only "canon" (I suppose?) characters are the NPC dragons in FR. All others are used for roleplaying and people can dress them up differently and use skins to personalize dragons beyond their color schemes and genes.
Note: Steven Universe and MLP characters are a huge gray area here too..
I think this excludes Transformers? Hasbro seems okay with people making Cybertronian OCs.
There's certain My Character/Avatar characters that cshould be allowed, and some that shouldn't. Frisk c an't be customized to look different-you just control their actions, versus a TERRA character you made that you made an OC from. If Frisk characters were allowed, there would be so many Frisk characters and they all LOOK the same. It would be kind of easy to steal art for them if your "OC" looks exactly like another OC (that is an MC but also canon). Fire Emblem's Robin and Corrin, too, fall into a gray area because they can be customized, but still stay true to a not-very-canon-divergent appearance, depending on the character's class.
There's a huge gray area that I think needs better defining.