She is a one-off character from this video.
Classic Anime Chara surprisingly does not have a voice, talking in the traditional MS Paint fonts, This is a reference to TylerAK412's Quotev story "Days with a Skeleton", in FNIA Chara Introduction. According to this story, Classic Anime Chara loves to murder, specifically trying to murder the protagonist and take over the story, Classic Anime Chara's motives, however, were scaled down to just wanting to murder everyone in the multiverse.
She quote unquote "dies" near the end of the video she appears in, but it is hinted that she is still alive, just as a puppet. According to Anime Chara herself, whenever Classic Anime Chara gets serious, the color scheme of her dialog changes from just green to green and yellow, aka the Chara color scheme.She then appeared as a cameo in this video as a corpse with the eyes torn out and bloodied, saying "Save me!" in her serious font near the end of the video.
She yet again appears in Attack of the one-offs, However, Her serious font is ruined because of paint.net, so her serious font is jumbled up, Anime Chara finally kills her, but it might not be the end of her.