The most significant modifications occur at the Pack-a-Punch machine , where players can spend to upgrade their current weapon. An upgraded weapon receives:

In , a popular zombie survival game on Roblox, "gun mods" primarily refer to the transformative upgrades available through the Pack-a-Punch machine and weapon customization in the Armory . Unlike traditional attachment systems, these modifications fundamentally change a weapon's stats, fire mode, and unique abilities. The Pack-a-Punch System

: Nails stick to targets and detonate after a delay. Stacking seven nails creates a massive "super detonation".

: The weapon is renamed and often gains a new visual appearance. Notable Weapon Modules

: Different mods and weapon classes have varying "Penetration Values" (ranging from Low to High), determining how many zombies a single bullet can pierce.

Upgraded weapons (also known as "PaP'd" versions) feature specific functional changes:

: Significant boosts to damage, range, magazine capacity, and reserve ammunition.