For halloween skins Riot could've thought of better skins for players to get :/ 
could've gotten a skin like from what i have thought of graveyard where his q is a pumpkin that comes out his passive stacks make a bat his shield is a coffin and his w makes a ghost underneath them and his ult when he hits the ground it makes graves instead of ice or whatever pop out
Dharc Kaisor1 votesOr make his shield a tombstone. Coffin or tombstone both fit.
Anywho, I feel that Necromancer 
is optimal for a new Harrowing skin. Change his soliders to zombies/skeletons (Maybe even both), give him some cool black robes (Or even make Azir himself a zombie) and then make his ult a line of tombstones. It fits pretty well, and actually makes sense since Azir was brought back from the dead according to the lore.
Anudaboi1 votesthats pretty cool but to bad riot doesnt make those :P stuff ever