Brood Queen

A Brood Queen is always the source of a Tyranid invasion. Four stout legs support a gleaming mess of capillaries that snake their way across its heaving hide. After a few seconds, the vague shadowy forms swirling through the inside of her near translucent hide crystalises into the vague outlines of miniature Avantai and Avanteen, no Draeen. Wrenching your gaze from the pulsing ever swirling mess of the Brood Queens womb you look up and stare into the coal-black eyes of her majesty the Brood Queen, her breath envelopes you carrying the sharp smell of acid with it - if you keep your mouth open long enough you will also ever so slightly taste is faint tangy flavour. Like the monsters, she spawns her spine arches upwards with spikes of brittle bone rearing up from beneath her thick hide tapering away to nothing on her long curling tail, which whips back and forth in unison with her wombs contractions.

Brood Queens dwell anywhere (except the oceans) though in recent times they have nested themselves in the bowls of space frigates and other large spaceships, leaving nothing behind once the infestation wins the upper hand. This is why they have become favoured methods of assassination and general warfare as they can rarely be traced back to the original instigator. The surroundings of the lair carry the sharp smell of acid - if a character keeps their mouth open long enough they will also be able to ever so slightly taste the air's faint tangy flavour 

On initiative count 20 (losing initiative ties), the Brood Queen takes a lair action to cause one of the following effects; the Brood Queen can’t use the same effect two rounds in a row:

• A tremor shakes the lair in a 60-foot radius around the creature. Each target other than the creature on the ground in that area must succeed on a DC 15 Dexterity saving throw or be knocked prone.
• A cloud of swarming insects fills a 20-foot-radius sphere centered on a point the creature chooses within 120 feet of it. The cloud spreads around corners and remains until the creature dismisses it as an action, uses this lair action again, or dies. The cloud is lightly obscured. Any target in the cloud when it appears must make a DC 15 Constitution saving throw, taking 10 (3d6) piercing damage on a failed save, or half as much damage on a successful one. A target that ends its turn in the cloud takes 10 (3d6) piercing damage.

Regional Effects

The region containing a legendary Brood Queens' lair is malformed by her constant spawning of new Tyranids, which creates one or more of the following effects:

• Deep gauges can be found in all but the hardiest substances, with faint traces of scratches even on these.
• Pools of acid resembling water dot the local landscape (1/2 a mile radius). The only indication of their foul nature is the noxious fumes that rise from them in warmer temperatures. If a creature drinks from these they take 7 (2d6) acid damage.
• Part of the ceiling collapses above one target that the creature can see within 120 feet of it. The target must succeed on a DC 15 Dexterity saving throw or take 10 (3d6) bludgeoning damage and be knocked prone and buried. The buried target is restrained and unable to breathe or stand up. A target can take an action to make a DC 10 Strength check, ending the buried state on a success.

If the Brood Queen dies, scratches remain as they have been created but the pools of acid fade over the course of 1d8 days.