4 to 5 players can enter a room (depend on the selected map), three are however required to start the match. Before starting a match or joining one, players may spend some GP (100-200) to buy some perks to make their task easier. Upon starting the game, a quick cut-scene will ensue and likely show the target that require protection, be it a space ship, etc. Difficulty settings resolve around ten (easy) and fifteen waves (normal). Hard difficulty is toggleable both with 10 and 15 rounds setting.
This mode works similar to original Zombie Mode, which pits players against an army of NPC Zombies each round. The biggest difference here is that players have a map-specific objective that they must protect against incoming horde of zombies in order to win the match. Upon spawning, all zombies will target the map objective, some completely ignore players' attack. Before each round starts, players will be notified of the total zombies as well as each type and their number that will appear on that round.
Players have their usual 2 lives to make it through 10 rounds (Easy) or 15 rounds (Medium), and they are free to use tokens / HypoMeds to support themselves. The map objective has a blue Lifebar on top of the screen which will drain as zombies attack it, and if it's reduced to zero, a cut-scene will show it exploding on the spot, failing the mission. Hard Difficulty works differently than in original ZM, throwing in more special (tougher) zombies and has the Lifebar limited to a certain point - if it falls below that mark, players will fail to get Hard difficulty prize and the round goes back to Normal difficulty.
Soldiers may buy tools to help them fend off the incoming hordes. By killing zombies, soldiers will earn Credits (Called Fuel ingame) to spend at the shop. By pressing the F-key (thus replacing the Berserk skill), a buy menu will appear with the following items, which can be purchased with credits awarded by killing enemies. They may only be deployed once each and soldiers are free to pick them up and deploy them elsewhere if so desired. If an item is already deployed but damaged, the menu will offer an option to fix it.
The tools available are likely to differ between each map, but these are the common one:
|Turrets/Sentry Gun||40%||Once set, it will target and shoot zombies on sight. It has a life-bar and can be damaged over time. It may also be upgraded and fixed in exchange of credits.|
|Decoy/Plasma Shocker||60%||Set up a device that attracts zombies toward it, distracting them away from the main objective. It has a life-bar and it can be fixed as well.|
|Claymore||30%||Once set on the ground, any enemies in its proximity range (front side) will trigger and make it explode, causing damage to enemies caught in the blast radius.|
|Airstrikes/Predator Missile||60%||Mark a spot on the ground and an airstrike drop will go straight to it, damaging any zombies in the blast radius. Any sort of movement cancel the call process.|
|Golden tickets that allows soldiers to pick up an additional prize at the end of match.|
|An item that gives an infinite reserve of ammunition, thus removing the need to refill. Also usable in classic Zombie Mode.|
Differently from classic ZM, Defence mode has a more complex reward system. It works similar to AI Ticket System, where players will earn reward box randomly when they shoot and kill zombies. Once each round finish, the reward boxes will be opened automatically, revealing the prize players have earned. At the end of the match (Normal difficulty only), there will be some Silver Slots for players to compete - after selecting it, the prizes will be revealed. Additionally, if players have any Gold Box Token, they can choose to open one of the Gold slots beneath.
Also a new feature called Combination Item System was introduced - some items comes with their own Cards which players can collect during the game. It can then be crafted into respective items (3d/7d only) using Gold Coins, amount depend on each item.
Being a new add-on for Zombie Mode, Defense Mode instead uses their own set of exclusive maps:
- This mode is quite similar to Plant vs. Zombies, a popular game on Mobile/Smartphone and PC platform, while the term "Fuel" used for the credits to buy the defensive tools was early used by an old Australian-made real-time strategy game called "KKND2: Krossfire" which also uses "Fuels" to construct new buildings, troops, and upgrades. Coincidentally, Krossfire is a close mispell on CF, further hinting the linking between two games.
- Unlike most other mode, the "E" command used to pick up tools are hard-coded instead of using "Defuse Bomb" command setup by players. Meaning players using arrow keys to play won't be able to pick up tools unless they reach out to the letters key or program their mouse/keyboard to simulate "E" key nearby.
- The reward system is quite different than classic ZM - for starter, high-grade prizes can only be accessed by buying Key Card (Cash item), leaving the Points System useless. Reward Boxes can no longer be saved and open all at once as all of them will open automatically upon earned during the rounds. Finally weapon prizes won't stack at all, making it impossible to earn them long-time. To compensate this, all reward weapons feature no damage bar so players won't need to repair them.
- It appears that the no-stack weapons are developer intended and SmileGate won't fix it - however, this poses a big threat that can glitch out players' storage if they exceed 655 pieces during the match (Newly dropped guns won't have spaces in their storage, and they can't be sent to Temp Storage anyway). As a workaround, a "Delete" button for junkie prizes (guns only) was added, so players can clear their storage easier. This button is often mislabelled as "Sell" however, due to most servers having no "Delete" button like CF China (Where free guns received on rank up can be deleted and won't give any GP back).
- In Z8 CF versions, this mode is called ''Zombie Mode 2.0''.
- In CFPH, it is called Zombie Apocalypse 2 or simply ZA2.
- In CFVN, it is called AI Mode 2 or simply AI 2.
- If players die at the ending of last match, they'll not get a chance to choose silver box at the end.