I have used this deck from the day i started clash royale to reach legendary arena.
Gameplay:
Offensive:Use the giant,valkyrie,wizard to attack.Preferably with the giant in the front.But this can only be done during the double elixir time,so you have to play defence until that time.Use zap if the opponent has inferno tower.
Defensive:Use fireball to take some troops along with side towers,or to take out minion horde.
valkyrie-To take down any ground troops,but positioning matters a lot so be careful.
bigminion-To take out mini pekka,knight etc.
archers-To take out small troops like goblin gang,goblins.
tornado-To push away troops like giant skeleton,prince,any pushing troops.
zap-To take out goblin barrel etc.