I think it's real but unfinished,the colouring looks off.
THAT final boss as a character is hype as fuck as everyone wanted to see him in his Prime before his "sickness". The problem is everything looks off which makes me think the leaks came from an old build.
Don't forget this. Elden Ring 1.00 is a completely different game than patched version 1.01. with literal reskinned malenia theme for bosses like Morgott or Godfrey etc. And even different attacks for bosses.
So wait till the dlc is out.
I'm gonna say it's real but unfinished and will be more grand on the finalized release version.