When playing a game with Illaoi, from the crit chance I got from tri-force, I noticed that I had massive damage when critting. From there I started to play full crit Illaoi, getting about 1200 damage crits. I wanted to see the highest amount of damage , so I went into a custom and got 3 IE, 1 ER, 1 Tri-force and 1 Maw. This gave me around 600 damage, and I also had 35% crit damage runes. I had thought initially that the massive damage was coming from an interaction with the bonus damage on W, but with this high amount of damage I noticed something game-breaking, which lead to the 4,500 damage crit.
When using W on a minion, I would deal about 2,000 damage to them. When I was standing next to them.
However, when I was at max range (I think it is about 400-500) I managed to get a 4,500 damage crit. This is when I realised that (this is what I believe the problem is) that When using W from beyond your normal attack range, you apply two auto's in one. Which means that with my setup, you effectively get (2.85 * 2 = 5.7) times + two sheen procs, which with Illaoi at level 18 is around 560 damage.
Whilst I was sad when I learned this was a bug, and I'll be sad to see it go, I feel like I have to let Riot know.