Game Mechanics

In the game

What raises it:

• A cell spotting you (most), and cells passing the alarm to their neighbours
• Every kill, a little more the more you've killed this run
• Getting hit, using your signature ability, and wrong answers in puzzle rooms
• Every cell currently hunting you, every second, plus a slow passive creep

What never raises it: the cells the immune system sends after you (hunter squads, Immune Siege and treatment cells, Killer T cells). Spotting you, hitting you or dying, they add nothing.

What lowers it: 5 seconds with nothing hunting you, then it drains steadily. Gear, strains and some traits make it rise slower.

The sections of the bar:

• 0–34: calm. Only the cells in each room.
• 35: first hunter squad. A tick on the bar marks it.
• 60: second hunter squad, bigger.
• 75: the host may take a treatment (a 30% chance every 10 seconds).
• 80: third hunter squad, bigger still.
• 100: Killer T cells are dispatched and hunt you from room to room.

A squad threshold only triggers again once Detection has dropped 20 below it.

In the game

A squad pours in through the farthest door, already hunting you. It's mostly neutrophils plus a B cell; from the Lungs on it adds a macrophage, and from the Bloodstream on an NK cell and a clump of platelets.

Every squad this run is bigger than the last (and deeper organs send more), and they get tougher with Immune Alert like every wave.

In the game

A warning sounds and a pack arrives at once. It follows you through every door, keeping its wounds, until it's destroyed. Its health shows in the top bar.

Each generation is stronger (+60% health, harder hits) and learns a new skill:

• Generation 1: a lunge at you
• Generation 2: + perforin rings
• Generation 3: + homing granzyme shots, and they come in pairs
• Generation 4: + at half health each one clones itself
• Generation 5+: packs of three, with wider granzyme volleys

They always move 15% faster than you, however fast your build gets, so you can't simply outrun them.

Killing one splits it into two smaller copies (they don't split again). The pack only counts as destroyed when every copy is dead. Only the originals drop a Killer T's own loot (materials, sometimes gear or an extra life, and RNA in Pandemic Game Mode); an elite copy still drops what any elite does.

After a pack is wiped out, Detection drops to 0 and can't rise at all for 20 seconds; the next, stronger generation comes the moment it maxes out again. While a pack is out, Detection can't spill over into another one.

In the game

Every 10 seconds at Detection 75+ there's a 30% chance (never during a boss fight). A coloured warning pulses for 2 seconds, then one of three doses floods the room:

• Antiviral (Tamiflu, or tenofovir for Retrovirus): drug capsules plus antibodies and neutrophils. While it lasts you fire slower.
• Booster shot (PrEP for Retrovirus): vaccine vials plus antibodies, B cells and plasmablasts. Cells take less damage while it lasts.
• Interferon: NK cells, antibodies, neutrophils and monocytes. You take more damage while it lasts.

Drug capsules and vaccine vials hang behind the swarm and support it; they're frail on their own. Survive or clear the dose for nucleotides, shards, sometimes a chaperone or an extra life. Each dose this run is stronger than the last, and the next one takes longer to come.

In the game

Alert rises by one step every 20 seconds of the run. Each step gives newly spawned cells 6% more health, makes elite cells more likely, and makes every hit on you 4% stronger.

In the game

From the fourth organ on, the Cytokine Storm meter (the thin bar with a hurricane under Detection) shows how far ahead your build is. It watches two things and goes by whichever is higher: how long ordinary cells last once you start hitting them (your last 24 kills; it starts filling when they die in under about 1.4 seconds and fills completely around a third of a second), and how much the fighting hurts you (damage taken in your last minute of combat: it starts filling when you lose under about a third of your max health a minute, and fills completely around 6%). It only reaches full strength once you have 6 traits.

It turns orange as a warning. Past its tick mark it turns red and the immune system responds: some newly spawned cells come ADAPTED, marked by a pulsing crimson halo:

• Up to 3× health
• Take up to 35% less damage
• Take up to 60% less damage over time (burning, poison)
• Move up to 80% faster
• Hit up to 60% harder
• Their hits pierce your defences: shields soak only 30% of them, armor (and Stone Skin) works at half strength, and room shields don't block them

Up to 45% of cells adapt at full pressure. Bosses, Killer T cells, antibodies and tumors never do.

STORM SURGE: if the meter stays full, every 20 seconds of fighting it surges a level higher, with no limit: each level, more cells adapt (up to 90%), and they get 40% more health and hit 25% harder. Ease off (or meet tougher cells) and the pressure drops again, ending the surge.

In the game

Immune System Level (the L number by the eye at the top):

• It starts at 1, goes up by one with every organ you reach, and by one with every Killer T generation you destroy
• Each new level is announced; higher levels mean the host's defences have matured

Learning your shots:

• Once Immune Alert reaches 3, the immune system watches your last 20 hits
• If 60% or more of them were one shot type, that type does 30% less damage until you mix it up

Remembering you:

• Memory B cells take half damage from the last shot type that hit them, until you switch
• Dendritic cells that keep you in sight for 2.5 seconds present your antigen: Detection jumps and every cell in the room is alerted, and then again every 4 seconds while they live
• Each Killer T generation comes back stronger, with new skills

None of this runs in the endless arena, where each set's own rules take over.

In the game

The first wave of a fight waits around the room unaware, wandering near where it started. A cell notices you if you come within sight (about 250 points with a clear line) or very close (85 points: it hears you). A cell that spots you alerts others nearby, with a '!' over each. A cell that loses sight of you for 8 seconds gives up the hunt. Retrovirus's Latency and some skills can make cells forget you.

In the game

Your auto-attack only targets unaware cells from closer in (210 points, instead of 380 for cells hunting you). A shot that hits an unaware cell deals 2.5× damage and shows AMBUSH. The hit alerts it, and it starts hunting you.

In the game

It targets the nearest hunting cell within 380 points (or an unaware one within 210), never through tissue, and leads moving targets. Extra projectiles fly side by side.

Influenza's Antigenic Drift changes the shot type every few seconds:

• Standard: plain shots
• Piercing: passes through cells
• Splitting: splits into two on a hit
• Explosive: bursts on impact and cracks armor

If you lean on one shot type too much, the immune system adapts and resists it a little.

In the game

You can't be hurt while dashing, and a dash carries you over pits. It recharges in about a second (gear, traits and skills can shorten it, and the Jet Stream skill lets it hold 2 charges). Dash-burst traits blast the spot you dash away from and leave a ring there that keeps hitting cells that follow you in; Transcytosis turns it into a teleport through cells and walls.

In the game

• SHIFT / LATENCY: your class's signature ability. It charges as you kill (bosses fill it faster) and raises Detection when used. Influenza's Antigenic Shift fires a burst of every shot type; Retrovirus's Latency hides you.
• ULT: your ultimate. It charges as you hit and kill cells; after using it, it can't charge again for 3 seconds (the button counts down). Every way of charging it faster (Lab, gear, strains, modifiers) still waits out those 3 seconds. Influenza's Pandemic infects everything nearby; Retrovirus's Integration Surge has its own effect.
• SKILL: the active skill you equipped in the skill tree (Viral Burst, Aerosolize or Seasonal Rebound), with its own cooldown. Augment skills in the same tree change how it works.

The Petri Lab upgrades the signature ability and the ultimate.

In the game

• Influenza A, the shapeshifter: Antigenic Drift rotates your shot type, Antigenic Shift fires every mutation at once, and Pandemic infects everything nearby.
• Retrovirus, the turncoat: cells its shots kill are stored in a reservoir, and Integration Surge releases them as allies that fight for you for a while; it deals 50% extra damage to bosses and Killer T cells, and uses Latency to hide.
• Filovirus, the hemorrhager: hits make cells bleed, Hemorrhage makes every cell nearby bleed, and Viral Hemorrhage hits every cell nearby hard.
• Halovirus, the superspreader: fast; Detection rises slower, spike volleys, Variant Surge and a Superspreader Event.

Every virus shares one lineage: the same level, skill tree, Petri Lab and gear. A generation's mutation decides which virus it is.

In the game

Cells roll a tier: white, green, blue, purple, orange, red or prismatic. Higher tiers have more health, hit harder, move faster, look bigger and drop more. Deeper organs and higher Alert make elites more common.

From blue up they carry affixes, named over their head:

• Swift: faster
• Armored: an armor bar to break first
• Shielded: a shield bar to break first
• Regenerating: heals over time
• Vampiric: heals when it touches you
• Volatile: bursts when it dies
• Splitting: splits in two when it dies
• Enraged: faster and fiercer below half health

In the game

A shield (cyan bar) soaks damage first; electric damage (from the M2 Ion Channel trait) tears through it faster. Armor (grey bar) is next and only lets part of each hit through; explosive shots crack it much faster. Health (red bar) is last.

In the game

• Burning (Pyrogenic Fever, Febrile Wake, flamethrowers): damage every second for 3 seconds
• Poison (NSP4 Enterotoxin, Toxic Wake, Mist Veil): stacks up to 10 times, more damage per stack
• Slow (Cold Adaptation, Cold Snap): each hit has a chance to slow the cell for 2 seconds; upgrades make the slow stronger, up to 60% (half on bosses). Slows never stack: a slowed cell can't be slowed again until it wears off
• Frost Aura is the exception: every cell inside it stays slowed, and it can freeze cells solid for a moment (never bosses)
• Electric (M2 Ion Channel, Ion Surge, lightning): extra damage that tears through shields

Apart from Frost Aura's freeze, nothing stops a cell outright: no stuns.

In the game

Critical chance (from gear, strains, effects and the High-Affinity Binding trait) makes a hit deal 2× damage and shows CRIT; critical hit damage (gear and High-Affinity Binding) adds to that 2×. Lifesteal heals you a share of auto-attack damage, once per shot, capped at 3% of the damage.

In the game

The boss room's doors lock until it dies. At 2/3 and 1/3 health it shields itself (break the shield first) and calls in reinforcements; in its final phase every attack is faster and also throws a ring of shots.

Bosses pick their attacks at random and aim where you're going, so keep moving. Beating one opens the passage to the next organ, drops a named set piece of gear (an ordinary piece in Pandemic Game Mode), materials and more. The last boss ends the run in victory.

In the game

Fight rooms lock their doors while cells are hunting you. The first wave waits around the room; later waves pour in already hunting. The top pill shows the wave and how many cells are left.

Clearing a fight heals 10% of your max health, about a third of the time leaves a mutation orb, sometimes a vesicle chest, and may bring a rival virus.

The minimap shows rooms you've been in and next to: white is you, red is unfinished, and special rooms and room tiers have coloured outlines. The boss room has a skull.

In the game

• Mutation Chamber: a free mutation orb and a chest
• Receptor Puzzle: step on the pads all at once, or repeat the order they light up in. Mistakes raise Detection. Reward: an orb, a chest, materials, sometimes RNA
• Trade-off Altars: take one bargain (something strong for a price) or walk away
• Mutagenic Pool: a random, often rare, trait for 20% of your current health
• Lysis Chamber: burst every host cell before the timer runs out
• Immune Siege: the doors seal and reinforcements keep coming; survive the timer
• Refuge: slip inside the cell to heal half your health, drop Detection and lose your hunters
• Gene Chamber: the key guardian and the gene it holds
• Tumor Room: a cancer (see Tumors & Metastasis)

In the game

Uncommon rooms get 1 boon; rare 1 boon and 1 drawback; epic 2 and 1; legendary 2 and 2; mythic 3 and 2; prismatic 3 and 3. Deeper organs roll higher tiers. They only apply while you're inside.

Boons: more nucleotides, weaker or slower cells, more damage, slower Detection, a guaranteed orb, chest or heal on clearing, more power-ups.

Drawbacks: fewer nucleotides, tougher, faster or harder-hitting cells, faster Detection, more elites, or acid that eats at you while you're hunted.

The minimap outlines each room in its tier colour, and the pause menu lists the current room's traits.

In the game

A sealed door (a mucus plug, tight junction or fibrin clot) often blocks the way to the boss or a treasure room. The gene that opens it is in a gene chamber you can reach without passing it:

• Mucolytic Enzyme (Nasal Passage, Gut, Bone Marrow): dissolves mucus plugs; mucus stops slowing you
• Fusion Peptide (Lungs, Liver, Brain): slips through tight junctions; your dash damages cells
• Plasminogen Activator (Bloodstream, Lymph Node): dissolves fibrin clots; platelet clots stop slowing you

A key guardian mini-boss holds the chamber, a different one in every organ: the Mucin Colossus (Nasal Passage), Syncytium (Lungs), Fibrin Weaver (Bloodstream), Reticular Warden (Lymph Node), Cajal Pacemaker (Gut), Polyploid Hepatocyte (Liver), Giant Osteoclast (Bone Marrow) and Betz Cell (Brain). Beat it for loot and the gene. Guardians deeper in are tougher.

In the game

• Abyss pits: falling in costs 35% of your max health; dashing carries you over
• Drop shafts: jump in to skip ahead
• Nerve endings (Nasal, Lungs): touch or shoot one and it sneezes or coughs, flinging everything nearby
• Cilia carpets (Nasal, Lungs): carry anything on them the way the arrows point
• Air sacs (Lungs): swell, then blow you and cells away
• Red blood cells (Bloodstream): solid, they shove you and block shots
• Reticular fibres (Lymph Node): slow you; two shots snap one
• Peristalsis (Gut): a wave sweeps the room and carries everything with it
• Bile ducts (Liver): spray a jet across the room after a warning line
• Stem cell niches (Bone Marrow): burst one to heal 12%, but neutrophils pour out
• Synapses (Brain): an electric arc fires between two neurons

In the game

Mutation orbs offer 3 traits and you choose 1. Orbs come from cleared fights (about a third), mutation chambers, puzzles, events and more. Each trait comes at a tier from common to prismatic; higher tiers are stronger. Traits last the whole run, and you can see them all from the pause menu. Some trait families only unlock as your virus levels up.

In the game

Five traits change how your shots behave: Endosomal Recycling (shots return), Neuraminidase Boost (pierce), Fomite Ricochet (bounce), Lytic Burst (burst) and Cell-to-Cell Spread (chain). Every pair of them has its own synergy, and you can hold any number: every synergy between your traits is active at once. Extra projectiles and Lateral Budding darts don't count.

In the game

When a run ends you choose 1 of 3 strains for the next generation, or 1 of 4 once a second virus is open (the left one always keeps your current virus). Strains change the rules for that generation's run: boons, curses or a mix. Your lineage records every generation; deeper skill tree rows need more of them. Abandoning a run doesn't end the generation.

In the game

Once you've reached an organ you can start a run there. To make up for the skipped organs you draft a head start: pick 6 traits from a larger pool, however deep you start.

In the game

Dormant Virions (rare drops from bosses, Killer T cells, rivals, tumors, treatments and chests) and the Incubation Period trait each give an extra life for this run (up to 3). Instead of dying you go dormant for a moment, then re-emerge with part of your health.

In the game

In regular runs they can drop from the first few cells you kill in a fight (never the last), so there's a fight left to use them on. Each lasts a few seconds:

• Spike Shield: invincible; run over cells to hurt them
• Chain Lightning: bolts chain between cells
• Fire Cross: four spinning flamethrowers
• Tidal Pulse: waves push cells back and wash away shots
• Gale Force: faster, and enemy shots blow back at them
• Stone Skin: take far less damage; boulders orbit you
• Frost Aura: every nearby cell stays slowed and may freeze solid for a moment (bosses never freeze)
• Mist Veil: most hits miss you; cells in the mist are poisoned
• Radiance: heal over time; bursts of light burn cells
• Umbra: a wide aura drains cells fast to heal you, drained cells burst into shadow novas, and your shots hit 60% harder

CRISPR, the rarest, makes you invincible and faster, and cuts apart every cell you touch.

In the game

Every run starts in a random host: usually a person, sometimes an animal. Every host has a tier and 2–4 hidden traits revealed when you infect it: some help you, some fight you. Animals carry their own signature traits. Some hosts also have a condition, like asthma or an immunodeficiency, that changes the whole run.

In the game

After you clear a fight, there's a 6% chance a rival shows up, at a random tier. Its health is in the top bar. There are three:

• Rhinovirus (the common cold): fast; darts around you firing spreads of shots
• Norovirus: slow; leaves slowing pools and fires rings of slowing droplets
• Adenovirus: armored; fires rotating crosses of fibers

Sometimes, and once when badly hurt, it breaks off and makes a run for the nearest door ("FLEEING!"). If it reaches the door, or you leave the room, it escapes.

An escaped rival can come back after a later fight (30% each time), one tier higher and a generation stronger, with a bigger bounty. Beat it for nucleotides, materials, gear (better the more generations it survived), maybe RNA and an extra life.

In the game

Most organs have a tumor room. Each organ grows its own cancer, with its own fight:

• Nasal Passage, Nasopharyngeal Carcinoma: nodules shield the tumor; destroy them, then the core
• Lungs, Adenocarcinoma: the tumor keeps growing and launches metastases; shoot them down before they take root
• Bloodstream, Leukemia: cancer cells keep dividing; thin out the escort, then kill the glowing stem cell
• Lymph Node, Lymphoma: clones hide among harmless lymphocytes; the core is only soft while it swells to split
• Gut, Colon Carcinoma: the core hides in crypts and surfaces in another; polyps drip caustic pools
• Liver, Hepatocellular Carcinoma: lobes feed and heal the core; kill them all before one regrows
• Bone Marrow, Multiple Myeloma: antibody spirals that lock on to you, and bone lesions in the floor
• Brain, Glioblastoma: tendrils creep at you and the core hops between glial nodes; cut the nodes down

The tumor grows on a timer shown at the bottom left (about a minute, a bit faster deeper in). Each tick it either grows a stage (more health, more satellite cells, faster attacks and shots) or spreads into an unexplored room (or grows a new one). Deeper organs let it grow and spread more.

Tumor room doors stay open. Cells you destroy stay dead if you leave and come back. Destroying it pays out big: nucleotides, a chest, an orb, chaperones, maybe RNA.

Leave the organ with it alive and it metastasizes: the next organ starts with a tumor at the same stage, still able to grow its full amount. Half the time the host gets radiation therapy: the tumor shrinks a stage, but you lose 20% of your max health and hit softer and move slower for 30 seconds.

A metastasized tumor sends squads of cancer assassins after you, wherever you are: a heartbeat warning, then nearly invisible cells that stalk you, mark a line, and pounce for heavy damage that also marks you to take more. Each squad is bigger than the last until the tumor dies. Every organ's cancer sends its own kind of assassin, each with a twist (see their entries).

In the game

Gear gives stats, abilities and sometimes set bonuses (bosses drop named set pieces, except in Pandemic Game Mode). It drops from cells (more from elites), Killer T cells, chests and bosses. Each tier only drops once you've reached its organ: green 2, blue 3, purple 5, orange 6, red 7, prismatic 8.

• Enhance: spend shards, chaperones and ribozymes to raise it up to +10
• Combine: fuse two of the same tier and slot into the next tier up, choosing which stats to keep; it keeps the higher enhancement level of the two (equipped pieces work too). This reaches one tier above anything that drops yet
• Dismantle: break gear down for nucleotides

Enhancing and combining can trigger a mutation. Your bag holds 150 pieces, shared by every virus.

The sixth slot, the Viral Genome, adds levels to skill-tree skills instead of stats (even past a skill's maximum); it belongs to no set and can't be enhanced or combined.

In the game

• Nucleotides (A, T, C, G): drop from every cell. G is the scarcest. They pay for Lab upgrades, combining and run modifiers
• RNA strands: unlock the advanced Lab upgrades and pay for skill tree respecs; they only drop in Pandemic Game Mode
• Shards, chaperones, ribozymes: enhance gear (each needed from a higher + level); ribozymes only drop in Endless Game Mode

In the game

Spend nucleotides on core stats, your signature ability and your ultimate. Most upgrades bring a milestone every 5 levels, with a major one every 10. Past the normal cap come 10 bonus levels, then hidden mastery tiers that appear once you max what's shown. Advanced upgrades need RNA to unlock first, and every third level of an upgrade also costs RNA, which only drops in Pandemic Game Mode.

In the game

Infect Game Mode runs and challenges earn XP: 1 per 3 kills, 8 per room, 150 for a victory. Each level gives a skill point (2 from level 10, 3 from 25, 4 from 40), and every rank of every skill costs 1 point.

• Three trees: Replication (offence, builds Viral Load), Transmission (movement and stealth, builds Momentum) and Persistence (survival, fills the Reservoir)
• Points you spend in a tree open its next rows: 5, 8, 11, 14 and 17 (the capstones need 21), and every skill in an open row can be learned; deeper rows also need a higher level, more generations and reaching later organs
• Each tree has an active skill for the SKILL button (Viral Burst, Aerosolize, Seasonal Rebound); equip one, and augments in its tree change how it works
• Shapes: circles are stats (dashed: on a kill), rounded squares only work in certain situations, diamonds are resources, octagons actives, hexagons augments and red-edged squares are risks with a cost
• Capstones (shield crests): pick 1 of the 3 in each tree
• Respeccing costs RNA. Some features also unlock as you level up. Every virus in your lineage shares this tree.

In the game

Craft them with nucleotides and materials, then load up to three before a run. Each has an upside and a drawback; some add a mechanic of their own, and certain pairs and trios unlock a combo bonus (see the Combos tab). Each run, in any Game Mode, uses up one of each loaded modifier; it stays loaded while you have more.

In the game

Challenges track kills, bosses, exploration, pickups, gear and more, some across all runs and some in a single run. Finishing one gives nucleotides, materials, XP and sometimes gear or skill points. Daily and weekly challenges refresh on their own.

In the game

Start by drafting 6 traits from a pool of 20. Sets start at 2 waves and build up to 5, with a boss set every few sets (any reached organ's boss, at least as tough as your deepest organ's boss and scaled to how much damage you deal). Every set rolls global boons and curses and is harder than the last. Clearing a set gives loot, some health back and a power-up pick. The arena is the newest organ you've reached.

In the game

Each city has six moments. Its standing policy is always in place. Every person you infect fills the city's gauge, and at 25%, 50% and 75% a political or medical response switches on (a city's response speed brings them forward or holds them back). At 60% its people answer with a social response. Once the city falls, its aftermath stays in force for every later run there.

Continents answer too, as a quarter, half and three quarters of their cities fall, and the world answers when 1, 3 and 5 continents have fallen. A continent's responses apply to every run on that continent; the world's apply everywhere.

A response is good for the virus (green) or bad (orange), and its card carries a category tag:

• MAP: the organ itself. A Refuge or a Lysis Chamber in every organ, fight rooms 30% bigger, +3 rooms per organ, mucus flooding every organ.
• CELLS: the immune cells. Hunter squads at 20/45/65 Detection, every cell spawning with armor, unaware cells patrolling the whole room, Killer T packs sent at 70 Detection.
• BOSS: the boss fight. Bosses shielding three times instead of two, arriving with elite bodyguards, losing their signature skill, or two bosses sharing the arena.
• TWIST: a rule of its own. Weather (rain slows every shot, fog shrinks your sight), a host that never takes medicine, 1 in 4 nucleotide piles being a 4× jackpot, a dash that teleports through walls.
• STATS: a plain bonus or penalty, such as +30% damage or 1 HP/s of regeneration.

Responses stack: a run in a fallen city carries the city's six, its continent's three and the world's. The run summary shows what switched on, and the next run there feels it.