In the last round, players have to defeat a new kind of Boss which is easy to avoid, but is smarter. There is an ability to place gun stands anywhere and call in airstrikes. Enemy weapons can not be picked up while fighting. Players are up against four kinds of enemies Scout, Paladin, Artillery and Heavy. Bots are of a secret military that have come to clean up the infection with leaving no loose ends. Human Campaign is a player and bot fight. On October 18th a new map was released with a sea monster boss. After a week, players under level 30 had access to the map. Players under level 30 were denied access to the map in the first week of its release. The bosses are "Pig Boss" "Voodoo Boss" "Devil Boss A" "Devil Boss B" and "Horn Devil Boss." This map was intended for players over level 30 and up. In May 2011, Nexon released a new map called "Dead Ends." There are five rounds with one BOSS for each round. After a set amount of time, normal zombies start appearing, creating an even harder challenge. This round presents a difficult Alien Boss with many different attacks. Once all the obstacles have been broken, a second round starts. Unlike the other Zombie Scenario maps, players can spawn at the nearest checkpoint if they die. The first round requires all players to break through obstacles while battling attacking zombies at the same time. Nexon Released a new map called "Last Clue" on January 27th. He is over twice the size of the normal Heavy Zombie, and holds a weapon that deals more damage than a normal zombie attack. A new zombie is revealed in this mode and called Zombie Boss. The levels keep getting harder with zombies having more health and abilities. You are able to buy extra health and damage if you have enough money.
The second new gameplay mode is Zombie Scenario Mod, which pits up to 10 players against increasingly harder waves of AI controlled zombies. Chinese zombie has the same power as the psycho one, but is slower and hard to target by humans. Bane zombie can put infinite obstacles to block bullets. The step mother zombie has the power to suck players towards her then turning them into a zombie when they are close. They are step-mother zombie, bane zombie and chinese zombie.
Three new zombies were released as well that day. The Hero is a female soldier armed with 8 shell Sawn-off that is as powerful as the original hero's weapon. The gameplay is the same as Zombie Mode 3 except that there is a different Hero. Zombie Mode 4 was released on July 4th in South Korea with it released in China, Hong Kong and Taiwan on July 6th. These zombies have higher health and different models than zombies infected after the Hosts. In all the Zombie modes, random players are selected to be the first zombies or "Host" zombies. Each level increases damage done by humans 10%. Each kill from his or any other weapon levels up the firepower strength by one level (there are ten levels total). The "Hero" will have the strongest unique weaponry (not purchasable) in the entire game. After 20 seconds, a random person on the human team will be chosen as a "Hero". For Zombie Mode 3, it basically holds the same gameplay as its precede, except that a firepower bar for both zombie and human teams are added. for example, the Singapore version has the normal zombie while China has the Psycho Zombie. The type of zombie that this is varies on where the Counter Strike Online version that you are using is released. In Zombie Mode 1 there is only one kind of zombie. These zombies are only available in Zombie Mode 2 and 3. There are a variety or different kinds of zombies, which are the Normal Zombie, Girl Zombie, Heavy Zombie, Psycho Zombie, Voodoo Zombie. When a zombie attacks a human, they become a zombie, and this keeps going until the time runs out, in which case the humans win or if all the humans become zombies. In Zombie Mode 2, everyone starts out as a human and gets 20 seconds to buy, hide and/or fortify their position, then a certain random player becomes a zombie, depending on the number of players present. The new gameplay modes: Zombie Mode 1, 2 and 3 are played between two teams, zombies and humans. A variety of other special items can also be bought with in-game points as well. Most special weapons, skins, power-ups, etc. Most of the weapons are "locked" by default, so GASH virtual cash or in-game points are essential to purchase them. The game also features a variety of additions over the International Counter-Strike, such as an introduction to female characters, numerous new weapons and skins for previous weapons. Counter Strike Online features some old game modes from the previous Counter-Strikes and new ones: Original mode, Death Match, Team Death Match, Zombie Mode 2, Zombie United Mode, Zombie Mode 3, Challenge Mode, Zombie Survival Mode and VIP Mode.