Pretty much an immobile version of the Tyrannocyte that is launched with even more powerful muscle spasms from the Hive Ships in order to bury and root itself into the ground like Ticks do into flesh. When burrowed, they release bacteria that pollute the atmosphere (the same way as Spore Chimneys do), and when threatened, it will roll out its five Deathspitters (or Barbed Stranglers/Venom Cannons if you don't mind paying extra) and vomit out Spore Mines or, in the case of Flyers, a Mucolid Spore. Added that the darn thing is a psychic resonator that strengthens the overall capabilities of Nids around it, pretty much paints it as a priority target if there are not more dangerous Tyranid Monstrous Creatures around.
Short: It's both planetary digestion unit, strongpoint and psychic relay for the Tyranids. All put in one package.
On The Tabletop
Sporocyst has a relatively decent statline of WS 5_+, BS 5+, S 5(4,3), T 6, W 12, I 3, A D6(D3,1), Ld 7, Sv 4+. Of course its low weapons skill and ballistic skill makes it a poor unit in combat, so it is best to support it with other units. Because of the short range of their Spore Nodes (9") and their ability to gain synapse, they're best deployed near objectives where your opponent will want to go, both to give you extra synapse near the objective, but also so it can lob spores at things.
Sporocyst comes armed with five deathspitters but can be replaced with either five barbed strangler or five venom cannons, depending if you want your Sporocyst to be good at infantry or vehicles, although it is still not recommended for the Sporocyst to fight on its own as it will be demolished if left unattended.
Interesting to note: The rules as written give the Sporocyst the Synapse ability AND keyword when it is within 12" of a creature with the Synapse keyword. So placing two Sporocysts within 12" of each other can keep each other's synapse ability going indefinitely (until one of them dies) once 'activated' by a single synapse creature walking within range.
|Leader Organisms:||Broodlord - Hive Tyrant - Swarmlord - Tyranid Warrior|
|Small Creatures:||Gargoyle - Genestealer - Hormagaunt - Ripper - Termagaunt|
| Biovore - Hive Guard - Lictor - Neurothrope - Pyrovore |
Ravener - Tyrant Guard - Venomthrope - Zoanthrope
|Monstrous Creatures:|| Carnifex - Dimachaeron - Exocrine - Haruspex - Malanthrope |
Maleceptor - Mawloc - Tervigon - Toxicrene - Trygon - Tyrannofex
|Gargantuan Creatures:||Cerebore - Dactylis - Hierodule - Malefactor - Nautiloid - Viragon|
|Flying Creatures:||Harpy - Harridan - Hive Crone|
|Bio-Titans:||Dominatrix - Hierophant - Hydraphant - Viciator|
|Other Organisms:|| Bio-Weapons - Cortex Leech - Mieotic Spore - Mucolid Spore |
Mycetic Spore - Spore Mine - Sporocyst - Tyrannocyte - Zoats