This game was recently released by supercell and features realtime multiplayer battles using Clash of Clans and new characters.
I have been playing it for a couple of days now and it is quite fun.
Here is a clip of some gameplay from a tournament supercell ran...
My only gripe with this game is the way to upgrade your army composition is to unlock chests. You can only hold a max of 4 chests at a time but silver chests take 3h to open and gold 8h.
This creates problems because you don't get rewarded with anything else when you attack besides trophies. I think this is an easy fix though - just reduce the time it takes for chests to open.
UNFORTUNATELY it is only currently available in Canada, Hong Kong, Australia, Sweden, Norway, Denmark, Iceland, Finland and New Zealand on the iOS.
They are using this as a soft launch/beta to see how the game goes but plan to release to more countries soon.
I think this is definitely a mobile game to keep your eye out for. Especially since the latest Clash of Clans update really messed up some crucial aspects.
Also here is the link to their website with more information: www.clashroyale.com