[Worlds 2019] Why is Ornn on the Worlds stage, and when should you use him in solo queue?

There have been almost 100 unique champs picked this year at Worlds, and in them is Ornn, The Fire Below the Mountain. But why is he being played after being silent all summer? And how can you use him yourself?

[Worlds 2019] DWG Nuclear: "Coach Kim told us that the real start of Worlds is from groups."

On the 7th, DAMWON Gaming took down Lowkey Esports in day 1 of the play-in knockout stages.