They're a bit cliché, but i really like evil versions of characters in fiction.
I am not just talking about protagonists, but characters in general.
Let me give you few examples:
Kusanagi, (KOF03, KOF02UM) Orochi Iori, Orochi Leona, Shiki Nanaya, (the Kagetsu Tohya and Melty Blood version) Akiha Vermillion, (Idk much about her, but i think that Akiha Vermillion in Melty Blood is also one of Tatari's creations like Nanaya, WArcueid and Kouma are) Red Arcueid, Sion Tatari etc.
I know that other people see them as unoriginal and not much effort put in them, i really like them, and i don't want to sound deep, but every person has a good and bad side to them so, that is why i have always liked evil version of characters in fiction. They express the other side of some character and can be sometimes more fun to play than the original counterparts. And some of them can be what-if? as well, which makes things more interesting. (Shiki Nanaya is pretty much a what-if? version of Shiki Tohno if he didn't have MEoDP, trained Nanaya Assassination Arts more, didn't fear killing others, and wasn't adopted by the Tohno family so, both are Nanayas, but one is not afraid of killing, meanwhile the other is the one you play as in Tsukihime and Kagetsu Tohya from his perspective, although the games treat him as if he's an biological family member of the Tohno family.)

(Kusanagi and Kyo are NOT the same person, but i still included him because i really like him, and i always thought of him as evil version of Kyo, even if it may or may not be true)
Spoilers:
Iori Yagami and Orochi Iori are the same person, Leona and Orochi Leona are the same person.
In Kagetsu Tohya, Shiki Nanaya appears as Shiki Tohno's nightmare, created from his fear of killing. He's one of Tatari's creations in the first two Melty Blood games. (MB2002 and MBReact have the same story mode)
In Melty Blood, Red Arcueid is one of Tatari's illusions, Arcueid is a vampire that doesn't s0ck people's blood and can go out in daytime without a problem so, Red Arcueid is pretty much Arcueid if she got crazy. Sion and Sion Tatari are the same person, because as far as i know, Sion Tatari is not a creation or an illusion, Sion turned into her when she got possessed by Tatari.
I am not too sure, but i think that Akiha Vermillion is one of Tatari's illusions as well, since you fight her in Melty Blood's story mode. However, in Tsukihime and Kagetsu Tohya, Akiha Tohno and Akiha Vermillion are the same person, as seen in Akiha, Hisui and Kohaku routes, Akiha Vermillion also appears in few comedy scenes of Kagetsu Tohya.