Grampy would kill miserable humans by waves. The first few would appear, they would die, and then the next and so on, up to a point where the enemies would reset and pop up again with more damage resistance. You can kinda guess the rest.
You are going to have a hard time finding ammo, but you better get started if you want to survive. Ammo is scarce, and if you thought we were going to give you recharging or endless firepower, you’re dead wrong.