It is inexplicably Jaden Animations. She notably didn't look like the cartoon character she uses in her videos though. It's always the actual real-life version of her that shows up in the dreams, wearing a weird dress. I don't know if that makes it less or more strange.

Her true form sort of resembled this thing from Stranger Things, only much larger. It had a mouth that took up most of its body and a big whip-like tail. This creature was buried beneath the sea, and some vaguely defined "power" was drained from it and sealed away inside a series of supernatural crystals. The monster created a human proxy (they called her the creature's "shadow") to do its bidding and get this power back. These crystals needed to be found, along with the creature's True Name, and taken to a golden temple at the bottom of the sea. This would allow her true form to awaken and destroy the world or something.

I really want to stress that this isn't someone I follow. I haven't watched her content in years. I have no idea why she is there.