The Skull series is the first anti-zombie weapon series to be featured in Counter-Strike Online built specifically to combat zombies. The weapons were developed by the Rex Research Institute in response to the zombie virus outbreak incident and have since started a long line of specialized weapons to assist in wiping out the undead. Although the successors to this series are the Balrog and Janus weapons, Rex Research Institute had recently begun engeneering more weapons for this respective series.
The weapons from the Skull series deal fatal damage to zombies through the use of specially augmented materials that were used in the development of the weapons. The results of the process gave the 5.56mm Anti-zombie, .50 Anti-Zombie, .45 Anti-Zombie, 12 Gauge Anti-Zombie cartridges and the blade of the Skull-9 extremely high firepower and penetration rate. Thus, all Skull weapons are very effective in dealing with zombies.
So far, there are 9 weapons in the Skull series:
- Main article: Skull-1.
SKULL-1 holds 7 of the special 50 caliber rounds for each magazine. It is a light-weight pistol and possesses a fast reload time and has two firing modes; semi-auto and full-auto fire. In the semi-auto fire mode, it possesses a higher accuracy and more damage. In the full-auto fire mode, it possesses a higher rate of firing. The special bullet developed by the government can give critical damage to zombie with its high penetration rate.
- Main article: Skull-3.
This is a submachine gun which holds 35 rounds for each round with special bullet of 45 calibers. It boasts with multi-purpose usage due to its good mobility, strong fire power with dual-mode and is equipped with silencer. The special bullet invested and developed by the government has a high penetration rate towards zombie and can deliver a vital damage to them.
- Main article: Skull-4.
An akimbo assault rifle based on the M14 EBR. This weapon fires 48 rounds of 5.56mm Anti-zombie bullets which deal critical damage to zombies. It has a usable scope that makes it useful in long range combat.
- Main article: Skull-5.
This is a remodelled version of M14 EBR which allows consecutive shots by equipping a scope. It holds 24 rounds for each round with a special bullet of 5.56mm. The special bullet which is developed and invested by the government delivers a vital damage to zombie with its excellent penetration rate.
- Main article: Skull-6.
Skull-6 is an anti-zombie machine gun fed with 100 rounds of 5.56mm Anti-zombie and equipped with a sniper scope for long range engagement. Its bullets develops superior penetration and do deadly damage to zombies.
- Main article: Skull-7.
Skull-7 holds 120 rounds each round with special 5.56mm bullet. To improve its accuracy in mid-long range, it is designed based on a structure that can reduce recoil while firing. The special bullet can give critical damage to zombies with its high penetration rate.
- Main article: Skull-8.
Skull-8 is a machine gun fed with 120 rounds of 5.56mm Anti-zombie and equipped with an axe bayonet below the barrel. Its primary fire can penetrate Kevlar and very good in dealing with zombies while the secondary fire can be used for emergency melee engagement.
- Main article: Skull-9.
The SKULL-9 is the melee weapon in SKULL series and it is made of special alloy material developed by the government. It has murderous destruction power, especially to zombies.
- Main article: Skull-11.
This is a specialized powerful shotgun with a special magazine which holds 28 rounds for huge sized zombies. It is also perfect for middle range battle since it provides an enhanced slug for its 2nd mode. The special bullet developed by the government will give critical damage to the zombies.
- This is the first anti-zombie weapon series introduced into Counter-Strike Online.
- The weapons possess color patterns that include different tones of yellow with black or dark blue.
- All weapons from this series can penetrate up to 4 objects and players with the exception of the shotgun Skull-11.
- All weapons from this series feature a crafted skull figure or art on them.