Gold is the standard currency in Royal Revolt 2. It is used for upgrading everything, from buildings, to towers, to units. You can buy hero items with gold in the Item shop, and gold is the only thing attackers can rob from a defending castle. You can buy it with gems.
Gems are the premium currency in Royal Revolt 2. They are used to buy some hero gear, as well as the majority of scrolls. The Alliance Tower is upgraded with gems. It's pretty easy to gain gems. They can be bought with real money, or be earned through leagues or quests. If someone uses gems against you in an attack, you earn some gems as well.
Pearls are used for buying items in the item shop as well as upgrading hero equipment. You get 3 pearls for each 10 gems you spend.
Vouchers are another currency used in the Voucher Bazaar. They can be traded for food, hero gears, gems, third spell and third troop slot, gold and workers.
Ninja Coins are gained by playing battles in Event matches battles , such events are the Ninja Event, Zombie Event, Yeti Event , Ninja Coins are also called as Event Coins or Event Currency , this currency is used to claim event rewards like Pearls, Event Troop, Magical Chests.