3Clash Royale card guide
Royal Ghost is invisible until he attacks and deals splash damage. He confuses the defense on offense.
Send Royal Ghost to the bridge to take out small troops and support cards; since he's invisible, your opponent has a hard time targeting him. P.E.K.K.A and bridge spam decks use him often. On defense he also helps against swarms.
Cards that deal with it efficiently:

This card has an evolution. The evolution is active in your deck’s 1st (Evolution) or 3rd (Wild) slot. The Evolution slot unlocks at Arena 3, the Wild slot at Arena 10.
ElixirDeck automatically takes your unlocked evolutions and heroes into account: build your decks.