I have some suggestions:
1- When Swain is in ult form, all of us we miss his monsterform, so I would add a bird head to him (his Tyrant skin has it!)
2- In his classic skin, the inside of his coat has a plane red which looks like unfinished. I would add some shadows to make it more realistic, like the outside.
3- When he uses E, he supposed to throw his demonic hand, so I would eliminate his hand from his 3D model until Q roots someone. This would add credibility and context, connecting lore and gameplay.
4- In his pirate and northern skin, the crows of his passive should be parrots and owls.
5- In his classic skin, i don't understand why he has a diferent clothes and chest in splashart and ingame.
6- I would make his autoattacks like bloody feathers (just his current aa, but with the shape of a feather, it would be a great tip)
Thank you for reading! :3