Couldn't the champion info screen be a simple solution for a sandbox mode?
I feel like instead of just showing a little video demonstrating a champ's individual abilities in the client, it could be a little interactive window to let you play around with its kit. I feel like that could be a way to get familiar with a champ's kit much faster than just watching a video. Maybe let you drop some Teemos around for target practice? Each Teemo killed equals 1 AD and/or 1 AP to your champ's stats, could help get a feel of their power without worrying about adding items or runes and whatever so it's not so complicated?
Is it a bad idea Riot?