There could be a New Troop called Dart Thrower that could throw darts to slow and damage defenses. At lvl 1 it could throw plain darts that just damage defenses. At lvl 2, it could throw poison darts to slow down the rate of fire. At lvl 3 it could throw ice darts to freeze the rate of fire for a second. At lvl 4 it could throw lava darts thta slow down the rate of fire and damage it continuously.