That looks like his fat layer bubbling up to the surface. Acid can cause fat to separate and rise to the surface. It would have not had enough time to truly eat down to his skull layer, so that checks out.
Fucking hell. That looks so painful. Each one of those blisters must feel like they are full of itchy hot sauce.
The teeth are on his left side, for artists needing a reminder.
I see accurate vein structure in the makeup. Holy attention to detail, well done!!!
It seems like, possibly, Simon's heart was starting to pump Ocean Blood at this point, causing his veins to darken, and possibly burn against its acidic nature. The inside of his body must have be literally on fire. Oh my god. No wonder they look like that. Using it as an early indicator of Simon's mutation as well? Chef's kiss.
I do think my only criticism is: why is it that the cartilage on his ears have taken so much damage, but not the cartilage on his nose? I'm aware of him needing to breathe, and the safety precautions pertaining to be being thrown around in a vat of thick liquid, but his nose is completely smooth and it's a little jarring. I assume it was a sacrifice of design they had to make to keep him safe, which is totally valid.
Some other things I can point out for writers looking for details:
Half of his beard is falling out (I assume they shaved it for prosthetic purposes).
Sclera of his eyes are turning grey
Skin between his cheek and the teeth-growths are actually still in-tact by the end, despite its thinning
Not sure if this was intentional, but it looks like his Eden tattoo is very visible by the end of the mutation. Was it growing back?
My blood science post for people wanting to read more about how the blood would work as an acid.
My post about the C.O.I. eating the blood.