Hello, my team and i recently came across a new way to get 8 champions for free. Ashe, Garen, Ryze, Annie, Warwick, Nunu, Master Yi, and Sivir.
Keep in mind this may only work for NA currently and Riot is offering this promotion starting January 22, 2016 through 11:59 PM, February 4, 2016.
Basically the price is set at 0.00 and all you do is Link your Amazon account to your League of Legends account. It took me 1 minute to do and the champions showed up on my account 20 minutes later. I think this is great for people who have Smurf accounts that need some extra champion variety.
I'm told if you live in Canada you need to enter a random US address for it to work. I hope this helps someone, see you on the Rift!
http://www.amazon.com/dp/B01AMD7HSW