Make a specialized tower with a good amount of hp, concrete armor, and good armor value, give it 2 attacks. One powerful attack against all ground units, preferably chaos type with AOE damage (you could use the orb of annihilation projectile for this.) And a second attack that does piercing type against flying units, make this attack really fast and give the unit a modified barrage ability that allows it to target multiple air units. Also make the tower self repair(give it a dummy ability named something like “auto-repair” while just giving it a small hp regeneration value) so the player wont be able to take it out easily by directing several attacks on it for this purpose.