Iiyiurg's appearance was similar to that of Iiyiug, except Greegeefied.
Differently colored overalls.
Red eyes, gloves, and mustache.
His nose and shoes turned green.
His glove had spikes.
One of his eyelids was drooping.
And due to the mental state he was in during the mutation, he was near brain dead, hence why he was drooling.
Because the mutation wasn't complete, Iiyiurg had no access to his powers. However, his brain, which was a battleground between Iiyiug's mind the effects of FFR, ended up emitting gamma, delta, radio, and X-rays for a 3 meter radius.
As mentioned before, the incomplete mutation caused Iiyiug/Iiyiurg to be near braindead, only capable of standing and softly moaning.
Iiyiurg wasn't 100% greature. The FFR wasn't able to take over Iiyiug twisted mind, thus making him unique.
He's the only being to be cured completely of the FFR, as well as subsequently gain immunity.
By curing his nephew, Borra2bi ended up REALLY pissing of Greegee, due to the fact he found a cure to the FFR (even though the cure itself was incidental, and was meant SPECIFICALLY for Iiyiurg. It's unlikely it could've cured a true greature.)