Make the tower model a Creep Tumor. And the attack animation Spawn Tumor. (Play Zerg and when you get a Queen (Spawning Pool First), use the Spawn Tumor spell and the tumor is the model, once you can, use the spawn tumor AGAIN (On the Tumor!!!) and it'll spew creep out at the specified location and change colors. Play the animation at -100% speed (backwards) and it goes back to original color to specify it's ready to attack again!)