Part 2!! Official translation edition (and a J -> E alias for strange klug to match with Strange Ecolo. i dont know anyone who uses the jp costume names but i will add them to the BUR if needed)
Okay, this one is not easy to explain, but I'll try my hardest.
The copyright of Puyo Puyo characters is a very, very weird thing. Sega owns all the characters, yes. But that was not always the case. Some of the Puyo Puyo cast was originally from Madou Monogatari. A game by Compile (now Compile Heart). Compile flew too close to the sun, sold the Puyo characters to Sega with the intention of buying them back once they were out of debt, did not get out of debt, went bankrupt. And now Sega permanently owns the Puyo franchise.
But just the Puyo franchise. There was still that giant Madou Monogatari shaped hole in the series that Sega legally could not fill. (Remember Compile Heart? They have the rights to (virtually) every Compile property, including Madou. Which means they were allowed to make Sei Madou Monogatari, a game full of legally distinct knockoffs of Madou characters (Aruru -> Pupuru, for one)
So coming back to the topic at hand... Sega owns the Puyo cast. Sega does not own the plotlines and stories made by Compile that are not apart of the mainline Puyo franchise. Where, finally, is where Doppelganger Schezo comes in. For the mobile game's 9th anniversary, Sega released a character named Dark Schezo. Taking inspiration from Compile Heart's legally distinct Puyo knockoffs, Sega decided to make their own. While Dark Schezo looks nothing like Doppelganger Schezo, reading his description paints a pretty clear picture that... yeah, this is meant to be D!Schezo. Explaining the plot of the game he's from (Waku Waku Puyo Dungeon) would make this post even longer, but all you need to know is that Doppelganger Schezo has the exact same character motivation, motifs (crystals), and general... doppelganger-ness. Every person in the fandom immediately recognized what Sega was doing. (Mostly because this was not the first time they had pulled something like this)
For all intents and purposes, this is the same character with a different design and a new name. Japanese fans have accepted that. Western fans have accepted that. Now it's time for Danbooru to accept that.
TL;DR Sega didn't care enough about discussing the rights to a character, so they just created a bootleg and figured nobody would notice. People noticed.
