PLAYER VERSUS ENVIRONMENT (PVE)
The list of Player Versus Environment (PVE) game modes in Counter Strike Online (CSO) or Counter Strike Nexon (CSN).
ZOMBIE SCENARIO 
The story begins after the zombie outbreak at the Rex Institute managed by Dr. Rex himself. New storylines have emerged as players progress through the chapters to discover and solve the mysteries surrounding the whole scenario.
Zombie Scenario remains of the most popular storyline-based game modes to date.
Up to 10 human survivors team up and complete objectives or break through barriers while battling waves of increasingly difficult AI-controlled zombies. To compensate, the maximum money each player can hold doubles from $16,000 to $32,000.
Players level up their firepower and maximum health points from killing zombies and destroying barriers. As a trade-off, the respawn time slowly increases, up to 60 seconds.
Ultimately, all survivors will face a major boss battle. Successfully completing the whole mission grants rewards and provides a summary of the players’ performance. Once the whole team is wiped out, they are given another chance to continue fighting.
Should they fail once again, the game ends in a failure.
HUMAN SCENARIO
Human Scenario depicts an ongoing battle between players and a huge group of computer-controlled human soldiers from the Vanguard organization.
There are three scenarios players have to survive, by annihilating a number of soldiers within the given time frame, surviving until the timer runs out, or reaching a targeted area or checkpoint.
The gameplay mechanic is very similar to Zombie Scenario, with a few notable changes. Players level up by killing enemy soldiers, which increases their maximum health points, firepower and the airstrikes’ effectiveness.
The airstrike is a unique feature available to each player. When using one, missiles launch from the sky, homing on enemies within the range. Higher level airstrikes provide better cover by launching more missiles on every call.
Health regeneration is also introduced, allowing players to gradually recover lost health points by taking cover from incoming fire.
Ultimately, the survivors battle a heavily-armored military vehicle in order to win the game.
Z-FILES
Z-Files, or Zombie Files is a single-player time-attack survival mode taking place in several locations throughout an unknown city.
Players take over the role of Senior Researcher Soi, an ex-employee of the Rex Institute along Dr. Rex before the zombie outbreak. Her task is to explore and discover top-secret documents kept hidden from the government all the while, as well as parties responsible behind them.
The game focuses more on the horror theme by introducing several key survival elements such as locating clues, limited stamina, and Quick Time Events (QTE).
While a room supports up to 10 players, it is a race against time to see who’s the fastest to complete.
HIDEOUT
Hideout, or the Play Room serves as a terminal for players to test drive their own weapons that are in their inventory.
The shooting range is divided into several lanes. Each lane has a dedicated interface for a player to spawn or generates a non-hostile zombie for target practice, and its behaviors are customizable (such as type of zombie, movements and behaviors).
There’s also a secondary terminal made for weapons to be tested on zombie bosses.
The next room is the Decoder room, allowing players to use their decoders and check out featured weapons. If a player manages to win any weapons featured, others are allowed to test them, especially those who don’t have them yet.
Open your decoders with your favorite characters here!