You’re probably neck-deep in zombie carcasses by now, and some of those zombie carcasses haven’t had the good sense to stop twitching yet. Enter the Galvaknuckles, a completely overpowered melee weapon here to help you double-tap those damn undead into oblivion.
Jokes aside, the Galvaknuckles truly are a really useful weapon as they can one-shot zombies up to wave 13 and don’t take up a weapon slot (so you can use them and still have two guns equipped). They can be purchased for a whopping 6000 points on the diner roof. Here’s how to get to the roof of the diner.
First of all, you need to find a rooftop hatch; this is found in a shed near the diner with a white door. Open the door with a turbine and the hatch should be inside.
Return to the diner and check the ceiling on the far end of the bar, you should be able to place the hatch there and gain access to the roof. Get to the roof by double-tapping the jump button under the hatch and turn around, the chalk drawing of the Galvaknuckles should be on the wall behind you.