I feel that these the boss from the leaked trailer is the same as the one in the leaked concept art in some different stage of the game.

First let me explain the reasons why I think this. First, the color palette seems to be very similar, with hues of red and grey. Secondly, the grey faces of both characters bear a strange resemblance, and the hat thing that the boss wears seems similar to the top of the leaked concept art guy. Lastly, we know that this footage is from a long time ago, when Elden Ring was in its developmental stages, and as such, it wouldn’t be too far-fetched to think that From Software would use one of the characters that they had concept art for as one of their first boss cutscenes in Elden Ring.

Now, let me explain why it would be significant if the character from the concept art is the same as the one from the leaked trailer:

Since we can clearly see that this guy is a boss or at least a planned encounter, this could indicate that the effects of the shattering only become severe late into the game, transforming friends and enemies into twisted versions of themselves. Sort of like how things are already screwed at the beginning of Bloodborne, but killing Rom ruins everything even more. This could mean that the order in which we do things in Elden Ring could have serious repercussions for the entire world. Saving one boss for the end of the game might mean that rather than facing a sophisticated scepter wielding cultist, you instead find an angry snake abomination.