Hey there,
not sure what has to be done for it, since the character Tyrael belongs to Blizzard, but there HAS TO BE a way to make a Tyrael Kayle Skin possible! In my eyes that even has the potential to become an ultimate skin, so ... JUST DO IT ! Have a look yourself! (check link)
If Riot makes an archangel skin that would be pretty cool.
They're not going to just copy another MOBA though, not just for copyright reasons, but also because copying another's design sucks compared to creating one yourself.
#NoPlagiarism
btw, i got the idea after i saw that new Caitlyn skin, which reminded me of Nova from Starcraft (also Blizzard)
yeah , much much need YES; GIIIEF PLZ -
