The X-04 Antithesis is an Antidote type assault rifle manufactured by The Antidote Brothers. Although not dangerous in and of itself due to its very poor fire rate, it has an extremely high pierce and a chance to cause a hit zombie to begin turning against its own kind. It is best used as a support weapon to cause chaos in large hordes, and to grant teammates a reprieve with packs of weak "allies".
- Deals 100 Antidote damage per shot. Pierces five zombies per shot. [RED] version increases damage to 225.
- Has a 10% chance to make a hit zombie gain the "Cured" status. Cured zombies will begin attacking regular zombies, and will be targeted and killed by their former comrades in much the same way. Large zombies and bosses are immune. [RED] version increases chance to 15%.
- Four rounds per second in fully automatic firing mode.
- 48 rounds of ammunition per clip. Reload time is 2.50 seconds.
- 12.0% movement penalty.
- Ammunition cost is 240 credits for 200 rounds of ammunition and 960 credits for 200 rounds of High Damage ammunition. [RED] ammunition multiplies cost by ten.
- The X-04 is designed based on the theme of the Antidote Bros manufacturer, which was originally created by Judbud.