This one got you! It's not a puffer at all actually, it's a filefish. Often goes by the name Mimic Saddle Puffer, and it's very good at mimicking Canthigaster valentini! This is actually Paraluteres prionurus however.
Wow, I really though it to be a close relative of Canthigaster valentini ! I would never having to search for it among the Filefishes... Thank you very much !
@vogelcommando It's a tough one, it threw me when I first saw one! If you look closely the little spines are visible in front of the dorsal, just laid flat. The filefish is also not quite as boxy as the puffer, but it's still difficult!