figi leather rot?

As some have noted, that doesn't look like a Fiji yellow. If it is, they can be seriously affected by stings (including by mushrooms).

In any case, cut the black spots off...ASAP. Whatever is happening can spread like wildfire otherwise.

 

Your kidding? Okay I can do that. I'm pretty sure its a very large yellow.

 

No. I'm not kidding at all. "Black Spots" on these guys can spread really quickly. They are usually only "skin deep" if you notice them quickly enough. Many times they can just be scraped off, without issue. Left alone, though, they can be pervasive. I have seen a leather be utterly destroyed in a week by them. The faster you can do this, the better. Scraping/cutting them often has much less of an effect on them than you would think (they might even be out playing again in five or ten minutes, although this varies).

OF COURSE, DO ALL CUTTING OUTSIDE OF THE TANK!!!!!!!!!!!

An exacto knife is a good thing to have handy if you have a bunch of leathers.

If this is, in fact, a Fiji Yellow, he/she more-closely resembles a flexibilis than a sarcophyton. The point here is that they can be more sensitive/difficult than other leathers. I always keep a closer eye on these guys/gals than the others. In particular, I make sure there is nothing nearby that can sting them, and watch their behavior more closely.

Otherwise, a stunning animal. Keep us posted.