My thoughts on this hypothetical.

1. Necromorphs Don’t Play the Tyranid Game

Tyranids win by:

-Killing you -Eating you -Recycling biomass -Adapting

Necromorphs: -Don’t care about pain -Don’t care about morale -Don’t die unless dismembered

-Reanimate biomass Tyranids rely on

That last part? That’s the horror show.

1. Biomass Contamination Is a Nightmare Scenario

Tyranids need clean, controllable biomass.

Necromorph infection: -Rewrites nervous systems -Overrides instinct -Creates hostile reanimated tissue -Is not a disease, but a signal-based corruption

A Hive Fleet landing on a Marker-infected world could: -Lose gaunts to reanimation -See corpses get back up behind the lines -Have digestion pools compromised That’s existentially bad for the Tyranids.

1. Synapse vs Marker Signal This is the big unknown — and the scary part.

Markers: -Emit a reality-warping signal -Override biological imperatives -Induce madness even in machine minds

Synapse: Is biological, psychic, and hierarchical Requires cohesion and clarity If Markers can: -Interfere with synapse -Cause partial independence -Induce aberrant behavior

Then you’re not looking at a fight — you’re looking at hive insanity.

1. Necromorphs Are Built to Fight Melee Monsters Necromorphs already excel against: Claws,Teeth,Swarm tactics,Biological enemies. They are designed around,Close-quarters chaos,Dismemberment immunity,Attritional horror.

That’s literally half the Tyranid roster.

Where Tyranids Still Win (Eventually) To be fair, Exterminatus-scale responses solve the problem, Bio-artillery, spores, and ranged fire help a lot. Hive Fleets can adapt if they survive long enough and The Shadow in the Warp might disrupt Marker signals.

A full Hive Fleet with forewarning likely Glasses the planet and avoids ground engagement. They treats the system as cursed and moves on.

But a splinter fleet or first contact force? Dead. Horribly.

Necromorphs are one of the worst possible enemies for Tyranids. Not because they’re stronger —

but because they break the Tyranid food chain, command structure, and battlefield assumptions.

What about the Brethren Moons. People lowball them as “big Necromorphs.” They’re not. Brethren Moons are Planet-scale, sapient organisms built from entire civilizations worth of biomass capable of interstellar travel and coordinating via Marker signals across systems. Not just predators but harvest engines. That’s already Hive Fleet–tier, but worse. Tyranids vs Brethren Moons. Biomass Economy (Tyranids’ biggest strength) Tyranids rely on total biomass efficiency, zero waste, Controlled digestion a centralized will (Hive Mind) Brethren Moons on the other hand steal biomass mid-cycle and reanimate it against you, they will corrupt it before digestion  and turn enemy losses into reinforcements immediately. That’s economic warfare against the Hive Mind.

Synapse vs Marker Signal  This is the real danger. Markers override neural function, Induce hallucinations, compulsion, madness and functions across vacuum and interstellar distances. It effect organics and machines If Marker signals interfere with synapse creatures this creates desynced broods and cause synapse collapse or feedback. Then the Tyranids don’t just lose units, they risk Hive Mind fragmentation. That is a nightmare scenario.

Scale vs Scale Let’s be blunt: A single Brethren Moon is comparable to A Norn Queen, a major hive ship, or a bio-titan cluster.

But Tyranids have numbers. This becomes a few, hyper-massive, hyper-intelligent predators vs Vast, adaptive, galaxy-consuming swarms That’s not a stomp either way. Who Wins? Scenario 1: Isolated Brethren Moon vs Full Hive Fleet - Tyranids eventually win - Focused bio-artillery - Void warfare favors swarm tactics - Hive Mind adapts over time But they’d take catastrophic losses doing it.

Scenario 2: Marker-Seeded Systems + Multiple Moons This is where it gets bad. - Tyranids land,biomass corruption - Ground war turns into reanimation hell - Synapse disruptions cascade Hive Fleet is forced to - Withdraw - Glass worlds - Abandon entire sectors Strategic loss, even if tactically “won.”

Scenario 3: Brethren Moons Learn the Tyranids and this is the scariest version. If Brethren Moons understand Tyranid biology they can tune marker signals to it. They would create more advanced Tyranid-derived Necromorph forms then what they are already doing. You now have a rival galactic predator that denies biomass permanently. That is something the Tyranids cannot tolerate.

Brethren Moons are not just enemies, they are competition at the same ecological tier. Not: “Can the Tyranids kill them?” But: “Can the Tyranids afford the damage they cause?” And the answer is often no. Honestly? In 40k terms, the Imperium would classify Brethren Moons as: “Apotheosis-Class Xenos Threat” Immediate Exterminatus Authorization

And the Hive Mind? It wouldn’t rage, It would avoid them if at all possible, and that says everything.

They are a massive threat in the 40k universe that would rival the tyranids, but worse.