A new item recently appeared in the item list of the official league of legends site. This might be an indication of a new champion with a mechanic similar to Viktor or just a new item. The item was only on the site for a short time, it was swiftly removed after that.
The reddit user Boxtop was able to take a screenshot
+20 Attack Damage (+2 per level)
UNIQUE Passive: Rengar collects trophies when killing Champions, and gains bonus effects based on how many trophies he has. Kills grant 2 trophies, assists grant 1 trophy, Rengar loses 1 trophy on death.