Experience

Experience is required to level up and evolve spirits. Experience requirements are the same for all spirits. However, the max level a spirit can reach varies.

To gain experience, you must spend less useful cards (i.e. materials) to enhance more useful ones. Materials that are not of the same type as the base (e.g. water, fire, thunder) do not grant as much experience as they would a base of their own type.

It's usually more efficient to level up materials before using them to enhance the base. For example, feeding one aqua slime to another would result in one level 3 aqua slime. Feed that to another level 1 aqua slime, and the new one will grow to level 6. Repeat once more and you have a level 10 aqua slime. Feed this to a water base, and it grants 150 exp rather than the 60 that you'd receive by feeding the four aqua slimes separately. As a bonus, it's much less expensive to feed spirits this way.

This strategy does depreciate for higher level materials, as experience given per level is fixed, whereas experience required to level up increases.

The following table gives the experience requirements for a spirit to level up from the previous level, as well as total experience required to level up from level 1.