Heroes of Ruin will feature a couple of leveling systems depending on the style of play but remain separate systems.
During co-operative play, the more the player plays alongside same person their friendship experience will grow, with more experience given the more the two players play together. However, it is not known how this alters the in-game experience in any way as of writing.
Character leveling remains a seperate feature of Heroes of Ruin, different from the Friendship experience. The leveling system of the character enhances their overall statistics, making them stronger and more durable. As well as giving them access to more spells.
Upon leveling up you can spend 'points' to increase skills you already have, or to purchase new skills for your available class.