Heroes

Heroes
The hero's bonus is applied both in offensive and defensive battles.

Heroes are a type of troop that provide a special bonus. Upgrading them costs an amount of crystals which progressively increases as the Hero level increases. They can be levelled up to level 100. They gain an additional troops from a given type under their command every 12 levels. The troop type varies from hero to hero.

Upgrading a hero costs the following amount of crystals (300 crystals altogether for level 100):

Level 1-20 - 1 crystal / level,

Level 21-40 - 2 crystals / level,

Level 41-60 - 3 crystals / level,

Level 61-80 - 4 crystals / level,

Level 81-100 - 5 crystals / level.

Mercenaries
You can also hire mercenaries to gain additional troops for your invasion battles.

The mercenary's bonus is applied only in offensive battles. Which is also why they are a lot cheaper than heroes. Mercenaries cannot be levelled up.