Is it part of a demon? Was it grown using demon blood? How does this give swain a demons power? Are demons usually powerful? Just gener knowledge on swains demon arm and the demon it came from as well as just general information on demons.
Swain's writer here. The arm itself is made of pure demonic magic, the same thing he shoots with his Q. It's held together by Swain's force of will and concentration. If you look closely, you'll see there's some opacity to it; it's not solid or grown.
The demonic magic, as a whole, holds Swain together, and helps him overcome the grievous wounds he suffered in Ionia. He has a leg brace and still carries a cane (i.e., has one on hand, just in case), because even a bad ass like Swain knows he can't concentrate 100% of the time. He is the type of man to prepare for contingencies.
The demon is a demon of secrets. It's why Swain hears whispers when he collects souls, and why he's haunted by visions of a dark future. Saying anything more is kind of against demon of secrets policy. [slayer-jinx-wink]
(Sleight edit for clarity above.)
I would not say the arm gave him demon powers, but it's the other way around: He got demon powers and the demon conveniently replaced bis arm. This demon works with information. We don't know much more about it.
We dont know a lot, outside of what is already obvious about the functionality of Swain's demon. We'll reveal more all in good time ;-) was pretty much the writing team's attitude towards the topic of Swain's demon.
Maybe we'll learn more about it with Mordekaiser's lore, but there's no guarantee it will be much if at all.
Don't think too much about it. It's there only to look cool.
The arm is actually Bad Dragon accessory that is nailed to a stub where his arm used to be. Apparently that was retconned according to @Interlocutioner.
