By clicking fuse button in the Army screen you can provide your creatures with great amount of exp. You choose the primary creature to gain exp and up to 10 creatures that will be sacrificed for this. Alternatively you can fuse creature with fruits. Doing this increase primary creature elite percentage instead. The most effective creatures to be fused are shadows. But fusing shadows costs a lot of gold, so you should consider using them in the mid-late game.
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