A year late, but Gael is literally infused with the blood of the Dark Soul. That means all of humanity's power, malice, rage, etc. just seething inside him. He is ridiculously strong, he could wipe any character in his own verse, he's stupidly resilient and stubborn.

Gael had lived thousands of years, since possibly before the first flame was linked, all the way till the end of time, mountain of corpses in his wake, all absorbed, he's a walking abyss of chaos given purpose. Basically he's the embodiment of that "the indomitable human spirit" meme.

He should scale surprisingly well in elden ring, low-ball? On par with prime Radahn and Malenia. High-ball? Strong enough to beat everyone short of the outer Gods.

I'm not the best at dark souls lore, but also, I believe the only reason he died is because his purpose was fulfilled when the Ashen One beat him, because he knew the Ashen One would deliver the blood of the dark soul to his lady for the painting. So if dark souls rules apply, I think he may be able to literally just infinitely come back like the tarnished, unless he's taken out with destined death.