Turtle Rock Studios made a big splash with Left 4 Dead in 2008. The online co-op shooter’s marquee feature was the AI Director, which adjusted pickups and enemy spawns based on how well players were doing. Left 4 Dead’s spiritual successor Back 4 Blood incorporates many of its predecessor’s features while also adding new ideas to the established formula.

One such innovation is Back 4 Blood’s Card system. These modifiers alter the game to make each playthrough unique. However, the feature may be a little opaque to first-time players.

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The game divides Cards into two categories: Active Cards and Corruption Cards. Back 4 Blood’s AI Director draws Corruption Cards every level, which influences things like enemies, weather, events, and rewards. Meanwhile, players play Active Cards that provide various perks and bonuses to help players survive the zombie hordes.

Back 4 Blood Corruption Cards

The AI Director chooses Corruption Cards based on the difficulty setting and how well the players have performed in the previous Acts and levels. There are four types of Corruption Cards in Back 4 Blood, depending on what they impact.

• Ridden (Common Infected) – Determine the frequency and behaviors of standard Infected types like Armored, Charred, and Blighted Ridden.
• Mutations (Special Infected) – Determine the frequency and behaviors of Special Infected like Breakers, Ogres, Snitchers, Hags, Tallboys, Singers, Reekers, and their various subtypes. Some cards will also add special modifiers like extra health or damage to a specified enemy.
• Challenge & Rewards – Special challenges that players can complete during the level. Back 4 Blood players who complete the challenges earn Supply Points and Copper depending on the difficulty of the challenge. Examples include but are not limited to retrieving blood samples, avoiding alarms, making sure all players survive, and escaping the level within a time limit.
• Events – Modifies the environment of the level. Examples include visibility reducing fog and power outages, an increased number of security doors, rapidly spawning Hordes, or an overabundance of a specific type of Special Infected. Some Event Cards are a combination of the above, such as an unusually large number of Snitchers inhabiting a blacked-out area.

Back 4 Blood Active Cards

After Back 4 Blood’s AI Director chooses its cards, players draw five Active Cards from their deck and play one. This allows players to select cards that will counter or mitigate the effects of the Corruption Cards. Some Active Cards are direct upgrades to a character’s stats and abilities. Others offer a powerful buff at the cost of some penalty. Back 4 Blood divides Active Cards into the following categories.

• Reflex (Blue) – Modifiers boosting the character’s speed, Stamina, and effectiveness in melee combat.
• Discipline (Red) – Modifies Ammo Capacity and Healing Efficiency and unlocks various items and abilities for healing and supporting other players. This category also has the most cards that unlock new starting guns.
• Brawn (Green) – Grants bonuses to health, damage resistance, and the effectiveness of melee weapons and explosives.
• Fortune (Yellow) – Mostly focuses on the player’s ability to gather ammo and Copper along with a few Cards related to health recovery and gun combat.

Players can unlock new cards either by finding them during a level or through supply lines. While some Cards are free, most Cards that players find in levels need to be purchased with Copper. Meanwhile, Back 4 Blood players can Spend Supply Points to open Supply Lines back at camp. Each Supply line is a series of progressively more expensive unlocks. Players start with one Supply Line but unlock more after completing it.

Back 4 Blood is out now for PC, PS4, PS5, Xbox One, and Xbox Series X/S.

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