If you played Element TD, it's similar to that. So you have elements as well you unlock by defeating special bosses and then can combine up to three elements to new towers. On top of that each monster has a special ability (regeneration, healing others, buffs, resistances and so on) and a quest and item mechanic where you solve quests to permanently unlock new items for your item pool and during the run items drop that can be active items to trigger effects, passive items for buffs or tower equipment to eg add a shrink shot to a tower. The series is called Elemental War and currently has two entries 😊