A Campaign?!
I think it would be amazing for the game. It would give an opportunity to let new players learn the mechanics of the game, without going PvP early. It could give you an opportunity to rework how bots work, giving more stages of difficulty, that would scale through the campaign. Give an opportunity to learn items more in depth. Give an opportunity to try lots of different Champs, so you know who you want to buy when you do go PvP. And I think gives a great opportunity to show off the lore. If you structure the campaign, based on the lore, playing through different Champs story lines. Can also fill in the missing pieces of the lore that seems to be missing. Just an idea! Please tell me what you think