Co-op Diatom Guide

What Co-op Diatom Is

Co-op Diatom is Pathogenic multiplayer mode where two to four players infect the same host simultaneously, each controlling an independent pathogen with its own organelle layout and plasmid progression. Diatom refers to the shared biological network linking party members—visualized as linked cells on the HUD—allowing coordinated revives, shared map discovery, and combo attacks when players Overcharge near each other. The mode works for full organ runs, Antibiotics dailies, and many challenge variants, though some restrictive challenges remain solo-only for leaderboard integrity.

Multiplayer does not simplify the game automatically. Enemy counts and elite spawn rates scale with party size, and bosses gain additional add phases designed to split team attention. Communication matters: call out T-cell beam directions, reserve dodge space for teammates, and agree before opening the editor mid-fight since pausing is limited in online sessions.

Setting Up a Lobby and Shared Rules

From the main menu, select Co-op Diatom, invite friends via Steam, and choose host settings: organ start (usually Skin), Antibiotics tier, and challenge modifiers if any. The host plasmid unlocks determine which challenge entries appear, but each player brings their own pathogen selection and graft preferences. Shared loot rules follow a need/greed hybrid—weapon organelles drop for individual pickup, while plasmid fragments and currency split among living members at room clear.

Revive mechanics require a living player to stand in a downed ally revive zone while clearing nearby adds. Macroke swarm wipes during revive attempts are the leading cause of party wipes. Assign roles early: one player focuses adds, another burns boss phases, a third keeps Mitochondria Overcharge active for teamwide buff nodes if you have Diatom synergy plasmids unlocked.

Build Synergies for Group Play

Complementary builds outperform four copies of the same artillery setup. Pair a melee Phagocytosis-tolerant frontliner with ranged Secretor backline, add a minion swarm player to clutter macrophage pathing, and include one flex Amoeba or Nanobot for editor repairs between rooms. Teamwide Mitochondria resonance—standing near allies during Overcharge—multiplies damage if everyone invested in co-op plasmid nodes.

Avoid graft layouts that rely on ballistic backward shots or chaotic pseudopod arcs unless you trust spacing; friendly fire rules are limited but visual clutter causes real dodging mistakes. Flagella movement upgrades help slower Helminth players keep pace in Lung airflow rooms. Share map information vocally even though fast travel (M) syncs for the party; split pathing on Intestine mazes saves time.

Scaling, Rewards, and Troubleshooting

Difficulty scaling adds roughly thirty to forty percent more enemies per additional player, with elite weighting increasing in Liver and Heart. Bosses gain shield segments or dual add waves that require synchronized Overcharge bursts. Antibiotics modifiers apply uniformly—co-op on high Antibiotics is significantly harder than solo on the same tier due to coordination overhead.

Plasmid fragments and challenge credit generally award each participant based on participation; AFK players receive reduced totals. Connection issues mid-run trigger a brief pause window for rejoin; if the host disconnects, migration rules depend on patch version—prefer stable wired connections for Heart and secret attempts. Watch the co-op video on this page for positioning examples, then practice on Skin and Intestine before tackling grouped Heart clears.

Latency, Roles, and Endgame Farming

Online co-op quality depends on host stability—Heart and secret organ phases amplify desync frustration when dodges register late. Wired hosts and region-aligned lobbies reduce rubber-banding during add-heavy boss transitions.

Define roles at lobby start: caller for T-cell beams, anchor for macrophage aggro, Overcharge timer for burst phases, and flex editor for Amoeba repairs between rooms. Undefined roles cause double-dodge or zero-dodge wipes.

Fragment farming in co-op rewards participation threshold—idle players receive reduced splits. Rotate who hosts dailies so everyone benefits from host-only challenge unlock visibility while still earning fair personal totals.

Additional Tips

Co-op rewards scale with communication quality—teams that call T-cell beams and Overcharge windows clear Heart faster than silent groups with identical builds.

Cross-reference related wiki pages for builds, controls, and walkthroughs rather than relying on a single article for full-run planning.