As of now, the "online" part of the game is making sure you can sync your game account with our servers to keep your progress save as well as buying Gold. It is a single-player game right now and will be enhanced with social features and hopefully ways to play together with your friends.
Of course we will put our heads together how to tackle balance issues in multiplayer, if it is feasible. There would of course be the need for some matchmaking mechanism, at least for player versus player combat.
By the way, good idea on the Demon spell there ;) We are definitely hoping that our players tell us what they would like to see in the future! Wouldn't it be awesome if we had a battle between an Angel, a Human and a Demon character in one arena? I sure hope we have your support so we can make this game awesome!