so its main weapon could be spellbooks or mage weapons dropped from enemies
spellbooks would need to very different from the normal staffs, so maby they have other properties eg: magma could spit clumps of lava out, earth could cause earthquakes, water could do little damage but remove the elemental resistance from the enemy
there are so many different books you could make

the towers it can cast could be like the mages but more status type moves
so one tower could poison and the enemy could take damage over time

one tower could be water and could remove resistance effect

if you have ever played kingdom rush origins there is a tower which creates earthquakes in the ground which does damage over a large area

im telling you if this charactor ever gets made i will buy it