The new hero gains 5% of the attributes of the sacrificed heroes. Therefore, it is beneficial to evolve heroes at the maximum level allowed (varies by hero). For most heroes of Epic quality or better, the maximum level for evolution is 100.
The new hero gains one star, up the to the maximum allowed (varies by hero). For example, combining two, 2-star heroes will result in one, 3-star hero.
The new hero begins at level 1.
The cost of the evolution ritual depends on the rarity of the heroes, as shown below.