Zombie Assault: Resurgence gives every merc three activated abilities, one for each class role, so there are nine in the whole game — three for Assault, three for Heavy and three for Medic. They are not bought with skill points any more: each one unlocks automatically when the merc reaches a set character level, improves passively every level up, and therefore scales all the way to the maximum character level. What you spend currency on is each ability's own upgrade tree, and that currency is BioMech CPUs.

How activated abilities unlock and upgrade

Every ability has two sequential Upgrades and four Enhancements, and the order matters:

  1. Upgrades are permanent once unlocked and sit under Improved Combat. They improve numbers such as damage, radius or duration, add utility effects, or strengthen the ability's core identity.
  2. Enhancements fundamentally change how the ability plays. You must unlock all Upgrades before the Enhancements become available.
  3. You can unlock several Enhancements but only equip one at a time. Two are available from the start, and the third unlocks alongside your Speciality.

Upgrades and Enhancements cost BioMech CPUs, which are found in higher-grade Strongboxes and earned through Bounties — the Strongbox page covers where that currency actually comes from.

Assault: Dash, Kinetic Burst and Adrenaline

  • Dash — a quick burst of speed to escape danger or jump into it.
    • Upgrades: Vicious Tackle (colliding zombies are knocked back, clearing maggots and scuttlers) and Critical Endurance (+10% resistances for 4 seconds after dashing).
    • Enhancements: Drop & Roll (removes damage over time and adds 20% dodge chance for 3 seconds) and Motion Munition (reloads the equipped magazine). Leaving Present and Marathon Man are Speciality-only.
  • Kinetic Burst — physical damage and minor knockback in a short-range 360-degree arc.
    • Upgrades: Explosive Additives (range increased to 4 m) and Tightly Packed Charge (double damage).
    • Enhancements: Stacked Charges (two additional charges with individual cooldowns) and Charged Burst (hold to charge up to 250% damage and range over 3 seconds). Holo Distraction and Exposed are Speciality-only.
  • Adrenaline — increases movement speed, rate of fire and reload speed for a short time, and reloads the clip on activation up to a maximum of 60 bullets.
    • Upgrades: Battle Ready (+10% critical damage) and Ignore the Pain (elemental resistances matching your other bonuses, with an added 10-second cooldown).
    • Enhancements: Deadly Thrill (kills heal 0.5% while active) and Murderous Retribution (enemies explode on death). Conserve Ammo and Team Confidence are Speciality-only.

Assault is the class that gets these three, and the other two kits work very differently — the class comparison is on the classes page.

Heavy: Hold The Line, Die Another Day and Orbital Strike

  • Hold The Line — while active, massively increases damage and pierce, gains aggro quicker and slows zombies within 5 m; stun length is halved.
    • Upgrades: None Shall Pass (+50% radius) and Moly Coated Bullets (+10% knockback chance).
    • Enhancements: One for All (teammates gain 50% of the buffs) and The Line is Drawn Here! (+25% damage and pierce but 50% slowdown). Blitzkrieg and I Can Do This All Day are Speciality-only.
  • Die Another Day — a huge short-term damage-resistance increase and a temporary increase to health.
    • Upgrades: Unstoppable (longer shield and health duration) and No Time To Die (temporary HP increased to 40%).
    • Enhancements: Forced Reversal (absorb the damage and release it as an energy explosion) and Last Stand (auto-triggers once per game when reduced to zero HP). Thunderdome and Unbreakable are Speciality-only.
  • Orbital Strike — calls in an orbital bombardment that deals huge damage and stuns surviving zombies.
    • Upgrades: Carpet Bombing (6 m radius) and Stacked Bombardment (+4 missiles).
    • Enhancements: Ray of Doom (replaces the missiles with a massive energy laser) and Napalm Strike (leaves burning ground with an extended damage-over-time effect). Lightning Storm and Resupply are Speciality-only.

Medic: Medkit, Haven and Biocleanse Bomb

  • Medkit — throws out a medkit that instantly heals any mercenary who picks it up.
    • Upgrades: Reinvented Medicine (+10% healing) and Magnetic Restoration (increased pickup range, kits float toward players).
    • Enhancements: Medkit Prep (can store one at full health) and Advanced Therapies (+20% additional healing). Fresh Start and Anti-Zombie Kits are Speciality-only.
  • Haven — places a field generator that forms a shield to reduce damage taken.
    • Upgrades: HAVEN 2.0 (7.5 m radius) and Static Shock (zombies entering take scaling energy damage).
    • Enhancements: Static Barricade (a hard-light wall blocks zombies and is destructible) and Protective Aura (follows the Medic at 75% speed). Energised Defences and Anaesthesia are Speciality-only.
  • Biocleanse Bomb — throws a gas grenade that poisons and slows down zombies caught in the gas cloud.
    • Upgrades: Curative Vaccine (minor heal over time for allies) and Viral Cure (enemies take +5% damage during the damage-over-time effect).
    • Enhancements: Contagion (kills spread the damage-over-time effect and stun nearby zombies) and Elemental Manipulation (-25% enemy elemental resistances, +25% team resistances). Preventive Remedy and Chemical Warfare are Speciality-only.

Medic abilities are the squad's sustain layer: healing teammates feeds the squad's objective XP, and abilities such as Medkit award XP for healing allies, so playing for the objective beats playing for the kill count in a group of four. The rest of the co-op rules are on the multiplayer page.

One equipped enhancement, many builds

Because each ability only has one equipped Enhancement at a time, the same class plays very differently at the same level. An Assault can be built for pure burst damage, for survivability or for relentless mobility; a Heavy can become a defensive fortress or a retaliatory bomb; a Medic can specialise in battlefield control or explosive support. The third Enhancement slot is where the Speciality choice comes in, and the speciality paths page lists what each branch unlocks.