Really liked the art and animation! Also liked the ability to delete spawners, that helps add to the gameplay/strategy
Could be interesting to explore this idea further.. For example, adding in some equivalent level up mechanic for the player too, where on level up they can perhaps choose a new minion type to spawn, or choose to upgrade a minion type, etc. Would also be nice to add more things for the player to do/control during the game (maybe adding some cooldown abilities, or the ability to control a minion).
Nice work overall!