Use the following trick to advance to rounds 5, 10, or 15 without killing any zombies. When starting, you will spawn in a narrow alleyway. From this position, face the junction and look at the walkway above to find the Shadow Man. Hit the Shadow Man five times with your default weapon or any other wall weapon to advance to round 5 with some points scored. You can shoot him five more times if desired to advance to round-10, also with more points. You can shoot him five times again to advance to round 15, also with more points, however he will now be gone