This suggestion may not be as important as some improvements but I personally would love for you to apply this suggestion.

The vast majority have different types of set: The main one, to get gold, for experience, for luck of chests …

For each type of set I have to use different types of combos and it becomes tedious to be changing the spells or units for each set, I would love that the combos can be saved in the letters ABCD, this way it could be easier to player.

We would choose different combos for each type of defense in a single click without the need to be looking for the spells