Originally Posted by
Ryllharu
Buff is not quite correct.
Predator was his original unique skill. That allowed him to pop open and absorb anything in close range, store it, and also mimic it.
Gluttony is the upgraded skill he acquired after the Great Sage ability to combine the Starving ability to...regenerate and eat anything from the Orc Lord he predated in the end of that battle. Gluttony added the ability to corrode things, and also increased the range on Predator.
Degenerate he acquired by using Predator on Shizu. It lets him combine skills, or tear aspects of things into different things, but in actuality seems to do whatever the story needs it to do, like protect Shizu from Ifrit for decades.