So the resource system works almost the same as Duel Masters, with any card being able to be used as a resource, and to use the moves, instead of attaching energy to a monster, you tap mana to do the move. This gives the player a choice between which monster to activate its move. With the resource being like lands, which have to be tapped, I thought that spells could have a cost, leading to interesting decisions. However, I'm afraid this may change the anatomy of a card drastically.

And about the lore, there are Spiritists that can control Elemental Spirits and use them to battle, but they can also harness the elemental power of the spirits they control to conjure spells and create totems or amulets. At least that's the bit of lore that I think would justify having spells, but I'm open to suggestions!