- "Full-auto submachine gun. Balanced fire rate with moderate recoil."
- — In-game description
- Ammo (Blackout): 9mm
- Operator Mod: None
The MX9 is a middling SMG that boasts mostly average characteristics. Its time-to-kill is about average for the submachine gun category, enabling it to edge out most assault rifles in close quarters with sufficient accuracy. Moderate damage coupled with a high rate of fire enable this weapon to win most engagements in close quarters. However, beyond close range, the MX9's recoil has a tendency to pull the sights off target, and can be difficult to control. This limits the weapon's effective range to strictly close quarters, although the weapon may win medium-range engagements in certain scenarios.
Handling is about average for the SMG category. The MX9 has no particular strengths or weaknesses in regard to reload time, raise time, or ADS time. The 35 rounds in the magazine can be expended rather quickly due to the high RPM, so spraying is not recommended unless as a last resort option. As such, the MX9 can struggle in prolonged gunfights, especially when taking on two or more enemies at a time. The iron sights are mostly fine for close-range engagements, but some users may find them cluttered, so the Reflex is recommended to improve usability.
The Quickdraw and Grip are strong choices, and both improve the MX9's ability to consistently win engagements. However, the AP Rounds and High Caliber fulfill more niche roles that aren't nearly as useful. In the case of the AP Rounds, submachine guns already have low base damage against vehicles and equipment, and other weapons, like assault rifles or light machine guns, are much better suited to an anti-armor role. In the case of High Caliber, the attachment is entirely dependent upon the user's ability to land headshots, and as accuracy is not the MX9's strength, the attachment is not as useful as on other, more accurate weapons.
The MX9 appears in the zombie maps Voyage of Despair, IX, Blood of the Dead, and Classified, where it's available as a weapon within the Mystery Box for 950 points. When upgraded via Pack-a-Punch Machine, it becomes the Nueve Muertes XX with the magazine size increased to 70 rounds and its ammo reserve increased to 350. It is unlocked for customization in the armory al level 25.
- ".40 Cal" is written on the side of the weapon, despite using 9mm ammunition in Blackout.