I think a champion with an Invisble Killer passive would be really cool.
The way the passive would work is that when the Invisible Killer champion killed another champ, the champs allies could not see that their ally died until he respawned. I know this would be pretty hard if not impossible to actually make in reality because of chat, and pings, but I thought it would be pretty cool. Name could be changed I originally used Unseen Killer but I thought that sounded to similar to Rengars.