Shaco's character

I think Necrit hit the nail on the head when he was spitting out ideas for the clown.

Instead of being just some "crazy (possibly person) with a mask", could be a great "Legend" type character.

are legendary creatures, who everyone in runeterra knows but only Magga has seen (and lived to tell the tale). They have surpassed mere existence and become immortalized in the legends of their world.

could work similarly, but instead of being the essence of death, he is the essence of Insanity.

While Kindred are death, Shaco is the voice in your head, whispering to kill everyone.

He is that person you see in the shadows, but is gone when you look again.

He is the demon jester.