The Immune System

Helper T Cell

Buffer

Hangs back and pulses cytokines that make every nearby cell faster and harder-hitting. A few helpers can keep a whole room buffed, so they're worth hunting down first.

• Stays at range while it buffs the crowd
• Buffed cells glow blue and hit harder
• Backs up the Follicular Helper T Cell boss

Thymocyte

Pack

Small, fragile young T cells that drift around you in packs. Every time you dash, every thymocyte nearby dashes straight at you too, so pick your dashes carefully.

• Circles you in packs instead of charging
• Copies your dash with a lunge of its own
• Some fail selection and die on their own

Lymphoid Progenitor

Grows up

Slow, weak and harmless at first, with a ring that slowly fills. When the ring completes, it grows into a full lymphocyte that's already hunting you, so catch it early.

• Keeps away from you while its ring fills
• Becomes a B cell, NK cell or helper T cell
• Now and then turns into a weakened Killer T clone

Follicular Dendritic Cell

Turret

A stationary cell sitting in a sticky web that slows you while you're inside. It fires rotating rings of slowing shots, so don't linger in its web.

• Never moves, but its web slows you
• Fires rings of slowing shots in every direction

Goblet Cell

Lobber

A Gut cell that lobs blobs of mucus at where you're standing. A warning circle shows first, then the glob lands and leaves a sticky puddle that slows you.

• Only walks closer when you're far away
• Step out of the warning circle in time
• Joins the Paneth Cell boss as reinforcements

IgA Plasma Cell

Ranged

A Gut and Liver cell that keeps its range and fires spreads of sticky antibodies. Each hit slows you, which makes everything else in the room more dangerous.

• Holds its distance while it can see you
• Fires spreads of slowing antibody shots

Stellate Cell

Area denial

A Liver cell that weaves toward you, leaving patches of scar tissue behind it. The longer it lives, the harder the floor becomes to move across.

• Drops scar tissue as it moves
• Scar patches slow you heavily for a while
• Joins the Kupffer Cell boss as reinforcements

NKT Cell

Stealth

Almost invisible while it stalks you. It appears with a '!' right next to you, lunges for heavy damage, then fades out again to line up its next strike.

• Barely visible until it's right beside you
• A '!' warns you just before the lunge
• Haunts the Liver, Bone Marrow and Brain

Megakaryocyte

Factory

A huge, tough Bone Marrow cell that keeps shedding platelet swarms and bursts a ring of fragments when you get close. Kill it to turn off the platelets.

• The toughest regular cell you'll meet
• Keeps budding platelets until it dies
• Hugging it doesn't work: it bursts fragments outward

Myeloblast

Rusher

Fast and fragile, it rushes straight at you, and when it dies it bursts into a few fresh neutrophils already on the hunt. Kill it from range, not point-blank.

• Rushes you head-on
• Bursts into neutrophils when it dies
• Fed in by the Hematopoietic Stem Cell boss

Astrocyte

Support

A Brain cell that hangs back and wraps nearby cells in protective shields, refreshing them as they break. It never shields bosses, but it can make a crowd much harder to crack.

• Stays at the back of the fight
• Refreshes shields on cells as they break
• Joins the Microglia boss as reinforcements

Resident Memory T Cell

Teleporter

A Brain cell that teleports right next to you every few seconds and fires a fan of shots with very little warning. Between blinks it only shuffles along slowly.

• Blinks in close from far away
• Fires a quick fan of shots right after
• Walks slowly between teleports

Killer T Cell

Mini-boss

A red, spinning cytotoxic T cell that stalks you, winds up and lunges at high speed. It never gives up the hunt, and every generation comes back bigger, tougher and faster.

• Swells briefly before every high-speed lunge
• Retrovirus deals extra damage to Killer T cells
• Drops rich loot, sometimes even an extra life

Generation 1

First generation

The first Killer T arrives alone with a single skill: the lunge. It's your introduction to the hunt, and a chance to learn its wind-up before things escalate.

• Hunts alone
• Watch for the swell, then dodge the lunge

Generation 2

Second generation

Still a lone hunter, but every lunge now ends in a ring of perforin shots fired in all directions, and the lunges come a little more often.

• Lunges end in a burst of perforin
• Dodging the lunge alone isn't enough anymore

Generation 3

Third generation

Killer T cells now hunt in pairs and fire homing granzyme shots whenever they can see you, on top of a bigger perforin ring after each lunge.

• Hunts in pairs
• Adds homing granzyme shots
• Perforin rings grow denser

Generation 4

Fourth generation

Clonal expansion: once badly wounded, each Killer T splits off a smaller clone of itself. The clones fade when the rest of the pack falls, so focus the originals.

• Still hunts in pairs
• Each cell spawns one clone when wounded
• Clones die with the rest of the pack

Generation 5+

Fifth and beyond

Packs of three with wider granzyme volleys and the fullest perforin rings. Every later generation keeps getting tougher, faster and quicker to lunge.

• Hunts in packs of three
• Wider volleys of homing granzyme
• Shots hit harder every generation

The Hunt

Follows you

Once dispatched, a Killer T pack bursts in from the far side of the room and follows you through every door, keeping its wounds, until you destroy it or reach the next organ.

• Survivors follow you into the next room
• A Refuge won't hide you from them
• Lose them by reaching a new organ or drop shaft

Split Copies

On death

Killing a Killer T cell doesn't end it: two smaller, faster copies burst out and keep hunting, and those split once more. Only the originals drop loot.

• One original can become a swarm of tiny hunters
• Copies are smaller and faster but hit softer
• The pack isn't beaten until every copy dies

Pack Destroyed

Reward

Wipe out the whole pack and Detection drops way down and freezes for a moment, giving you room to breathe. The immune system then trains a stronger generation for next time.

• Detection drops and briefly freezes
• The Immune System Level rises
• The next generation comes when Detection maxes again

Medical Treatment

High Detection

Once Detection runs high, the host may take a treatment. A tinted warning pulses over the room, then the dose arrives: survive it for a reward, or walk out of the room to escape it.

• Never happens in a boss room
• Doses grow bigger as the run goes on
• Escaping skips the fight but forfeits the reward

Antiviral Dose

Dose

Drug capsules flood in with antibodies and neutrophils, and the drug in the blood slows your firing for as long as it lasts. Retrovirus faces an antiretroviral version instead.

• Brings capsules, antibodies and neutrophils
• You fire slower while it lasts
• Each virus gets its own real-world drug

Booster Shot / PrEP

Dose

Trained antibodies, B cells and plasmablasts rush in, shielded by the vaccine, and every immune cell takes less damage while the dose lasts. Retrovirus gets PrEP instead.

• Arrives with vaccine vials or PrEP capsules
• Every immune cell gets tougher for a while

Interferon Shot

Dose

Interferon puts the host on high alert: NK cells, antibodies, neutrophils and monocytes swarm you, and every hit you take lands harder until it wears off.

• NK cells form the core of the dose
• You take extra damage while it lasts

Radiation Therapy

Cancer

When cancer spreads into a new organ, the host may answer with radiation. The tumor shrinks a stage, but it scorches you too and leaves you sick for a while.

• Can strike soon after a metastasis arrives
• Costs you health but can't kill you
• Radiation sickness weakens and slows you

Oseltamivir (Tamiflu) Capsule

Medicine

An antiviral capsule that hides behind the nearest crowd of immune cells inside a wide cloud. Inside the cloud you fire and move slower, and it keeps healing the cells around it.

• Appears in every run except Retrovirus
• Heals every immune cell in its cloud
• Hits Influenza A's fire rate hardest

Tenofovir Capsule

Medicine

Retrovirus's own antiretroviral capsule. Inside its cloud you fire and move slower, and the immune cells around it get a speed boost.

• Replaces the Tamiflu capsule in Retrovirus runs
• Makes nearby immune cells move faster

Influenza Vaccine Vial

Prevention

A vaccine vial that trails the crowd from behind and projects a large protective ring. Immune cells inside it take only a fraction of your damage.

• Appears in every run except Retrovirus
• Has no touch attack of its own
• Protects every cell inside its ring

PrEP Capsule

Prevention

Retrovirus's protective capsule. Every few seconds it wraps the immune cells inside its ring in fresh shields, so the crowd around it keeps getting tougher.

• Replaces the vaccine vial in Retrovirus runs
• Shields every cell inside its ring

Hiding Behind the Crowd

Medicine AI

Drug capsules and vaccine vials work from the back line. The more immune cells around them, the tougher they get, but caught alone in the open they're very frail.

• They tuck in on the far side of the crowd
• They back off when you get close
• Thin the crowd or catch them alone

How Elites Roll

Overview

Every regular cell rolls a tier as it spawns. Deeper organs and a higher Immune Alert make elites far more common, until nearly everything you face is Rare or better.

• Elites are rarer in the Nasal Passage
• Rare and up wear a name tag with affixes
• Bosses can roll tiers too

Swift

Speed affix

This cell moves much faster than a normal cell of its kind, on top of any speed its tier already gives it. Cells that can't move never roll it.

• Stacks with its tier's speed
• Never on cells that can't move

Armored

Armor affix

Carries a grey armor bar that has to be broken before you reach its health. Armor soaks a lot of each hit, but explosive shots crack it much faster.

• Grey armor bar above its health
• Explosive shots crack armor faster

Shielded

Shield affix

Wrapped in a cyan shield bubble that soaks damage before armor or health ever take a hit. Electric damage tears through shields faster, so it's worth bringing some.

• Cyan bubble breaks first
• Electric effects shred it

Regenerating

Healing affix

Heals itself whenever it's left alone for a moment. It can't out-heal steady pressure, so once you start on it, don't leave it half-finished.

• Heals only when nobody is hitting it
• Steady damage keeps it down

Vampiric

Lifesteal affix

Heals every time its touch hurts you, so the longer it stays on you, the harder it is to put down. Bosses with this affix heal far less per touch.

• Feeds on contact damage
• Weaker on bosses

Volatile

Death blast

Bursts in an explosion when it dies, hurting you if you're too close. Finish it from range, or your death card will read CAUGHT IN AN EXPLOSION.

• Explodes on death
• Keep your distance on the killing blow

Splitting

On death

Splits into two smaller copies when it dies, and both come out already hunting you. Bosses, Killer T cells and cells that can't move never roll it.

• Two smaller copies on death
• Copies hunt you right away

Enraged

Rage affix

Turns red and fiercer once it's badly hurt, moving faster and hitting harder for the rest of the fight. Cells that can't move never roll it.

• Kicks in when its health runs low
• Faster and harder-hitting when ENRAGED

Awareness & Stealth

Stealth

A fight's first wave waits around the room unaware, wandering near where it started and sweeping a visible sight cone. Stay out of sight and you get to pick your fights.

• Unaware cells show a tinted sight cone
• Getting spotted alerts nearby cells in a chain
• Hunters that lose you eventually give up

Ambush

Sneak attack

Catch a cell unaware and your shot hits much harder, marked AMBUSH. Your auto-attack waits until you've crept close, and unaware kills raise Detection less.

• Sneak close before you open fire
• The hit alerts the cell
• Quiet kills keep Detection lower

Detection

Eye meter

The eye meter at the top right tracks how aware the immune system is of you, shifting from calm green through yellow to pulsing red as things heat up.

• Spotting, kills and hits all raise it
• Fills slower in the early organs
• Cools off once nothing is hunting you

Detection Thresholds

Escalation

Each section of the meter brings a bigger immune response: first hunter squads, then a chance of treatment, and finally Killer T cells once it fills completely.

• Hunter squads grow bigger with each step
• Treatments become possible once it turns red
• A full meter sends Killer T cells

Hunter Squads

Reinforcements

Cytokines call in a squad of cells that already know where you are, entering through the door or corner farthest from you. Each squad in a run is bigger than the last.

• Mostly neutrophils backed by a B cell
• Deeper organs add Macrophages, NK cells and platelets
• Grows tougher as Immune Alert climbs

Cooling Down

Lower Detection

There are several ways to bring Detection back down and shake hunters off your trail, from resting in a Refuge to solving receptor puzzles.

• Refuges heal you and make hunters lose you
• Receptor puzzles and Retrovirus's Latency lower it
• Destroying a Killer T pack freezes the meter

Immune Alert

Run timer

A fever that keeps rising as the run goes on, shown by the flame in the HUD. The longer you take, the tougher the whole immune system gets.

• New cells spawn tougher as it rises
• Hits on you get stronger too
• Raises the odds of elites

Fights in Waves

Waves

Fights come in waves: a big placed wave that starts unaware, then smaller reinforcement waves that pour in already hunting. Bigger rooms and later organs add more waves.

• A progress pill tracks each wave
• Reinforcements spawn away from you
• Every wave brings an antibody swarm

Immune System Level

Host level

The host's defences mature over a run, shown as a level beside the Detection eye. It rises as you reach new organs and destroy Killer T packs, and it sets how big treatment doses get.

• Rises with each organ and Killer T pack
• Shifts from green toward red as it climbs
• Shown once the immune system starts learning

The Immune System Learns

Unlocks later

Lean too heavily on one shot type and the immune system starts resisting it, with a HUD warning to tell you. Mix up your shots and the resistance fades.

• Kicks in once Immune Alert starts climbing
• Influenza A's Antigenic Drift and Shift counter it
• Switched off in Endless Game Mode

Immunological Memory

Memory

Several cells remember what you did to them and come back better prepared, from Memory B cells shrugging off your last shot type to Killer T generations returning stronger.

• Memory B cells resist your last shot type
• Dendritic cells present your antigen to the room
• Each Killer T generation learns a new skill

Cytokine Storm

Unlocks later

A thin hurricane meter under Detection shows how far ahead of the curve your build is. Kill too fast or take too little damage, and the immune system answers with adapted crimson cells.

• Never kicks in on a fresh run
• Turns red and pulses past its tick mark
• The Lymph Node runs a stricter storm

Adapted Crimson Cells

Storm response

Past the storm's mark, some new cells arrive ADAPTED, wrapped in a pulsing crimson halo. They're tougher, faster, harder-hitting and built to punch through your defences.

• Resist burning, poison and bleeding
• Their hits pierce shields and armor
• Bosses and Killer T cells never adapt

Storm Surge

No cap

If the storm stays full, it keeps surging higher the longer you fight, with no limit. More cells adapt and the crimson ones grow tougher with every surge.

• Each surge makes crimson cells more common
• Adapted cells hit harder every surge
• Drop below the tick mark to end it

Cytokine Buffs

Buff

Helper T cells and Basophils pulse signals that rile up every cell around them, making them faster and harder-hitting. Buffed cells glow blue, so you can spot them.

• Buffed cells glow blue
• Basophil pulses swell you up too
• New pulses refresh the buff rather than stack

Deeper Organs, Tougher Defences

Escalation

Every organ's immune cells have more health, hit harder and move faster than the last, and the Brain hides behind a blood-brain barrier that shrugs off part of your damage.

• Nasal Passage cells hit softer while you learn
• The blood-brain barrier blunts your damage
• Infect Game Mode toughens cells beyond your starting organ