Storyline:

"Teemo! I need backup!" - Tristana "On my way!" - Teemo Teemo says as he rushes to the rescue. Looking up, the sky turns gray-black. Flames starts corrupting the city. Ash start falling from the sky as the yordles wonder... is this the end? As Teemo approaches the border of Bandle City, he sees Piltover's Army, ready to strike. "Code 234! We need all... yordles... for this battle."

It explains it all here! Would loveee these skins!