New purchasable characters/ teams

I need to suggest one thing which cal let all players be more compatitve to the game. Always a new player appears by keys and its very hard also to find the best troop. Why not make a new characters with super power also to be purchasable for a limited time? At least weekly. Some of them can be also one color mana and also different mana.
The game will become more fire. Also the price will defere from characters according to their features.