Something that's really been bothering me is what kind of missions that one can run with the Tyranids, because to me they seem like an enemy that you can't really run missions against like the Tau or Chaos. Any ideas or experiences because I would love to make a Tyranid focused game, but I just can't understand how that would work out.

Hive ships have been detected entering the system of several agri-worlds. The capitol is an important part of Medicae and the Magos Biologis, its loss will cripple the crusade and have far reaching consequences that cannot be fully realized now. And the swarm seems to know this. They bypass the outer worlds and their resources going straight for the capitol and the hospital facilities there. Its not about just saving the lives of the Magi and the Doctors the loss of equipment will be too much. That world must not fall, cannot fall.

The Watch-Captain has ordered the Kill-Team and a flotilla from the Battlefleet into the system to stop the Tyranids. If the world falls millions of Imperial Guard and others will die. By the God-Emperor it is not a full Hive Fleet and a rather small fragment at that. They need to stop it now before it can call for reinforcements since the Hive Mind saw it has relatively undefended. The relatively unguarded worlds with a rich bio-mass will swell this fleet so it can consume a thousand others. And the research there will give the Hive Mind a future edge.

First mission eliminate the Fleets ability to signal for help from the rest of the Hive Mind. This could involve boarding the Hive Ship and attacking a specific set of creatures. Or something that relays the will. Almost like a Synapse creature for the ground forces. But I also realize the Hive Ship is an embodiment of the Hive Mind so this part would need to be handled by each GM to what they felt was right. As they are fighting to stop the Hive Mind for sending a request to its parent Hive Fleet the vanguard creatures disable planetary defenses in a small grid directly below the Hive Ship.

Battles raging everywhere they drop with the swarm to disrupt the first seeding enough for someone to get those generators back up. Without those defenses the world will fall. Now the generator can be repaired off screen if so desired or the transport carrying the crew is shot down and the Kill Team needs to escort them to the generator. This means they need to break off their actions which will allow the Hive Mind to consolidate their forces but with the defenses reinforcements will be coming a lot slower.

When they arrive at the generators the doors are sealed by "defenders" have already taken up positions around it and are trying to cut through the doors. I wouldn't let on right away these are Hybrids of the Genestealer cult. Let the colonel or whoever be acting weird. Even though this breaks with what GW has said before let the Colonel speak with a million voices at once. Something the Hive Mind has never done before. Give the PCs a reason to redouble their efforts to defeat the fleet here and now.

And of course the rest of the game would be about countering the Hive Ship and learning about the creatures. Perhaps even having them killing the guiding intelligence of the ship so that the Imperium can study and learn it. Or what if they defeat the ground forces but the Imperial Navy destroys the Hive Ship and it seeds the planet below. Those spores and colonies burrow beneath the ground. Months later they receive a message from the world calling for aid. When they return they find the Tyranids without the guiding will of the Hive Mind all through out the world. Different mound like structures dot the world each fighting humanity and the other hives for dominace.

Possibilities are endless!

They certainly are more combat-focused than Chaos/Tau, because you can't reason with them and there's less chance for ongoing antagonist leaders with distinct personalities…though you can wing it with a nid, I'd play it sorta like the Spinosaur from Jurassic Park III, always lurking and trolling somehow.

There can be political drama with trying to maneuver assistance from other Imperial forces, deciding between rescuing people in the path of a tyranid attack or mass-murdering them to prevent their biomass from being collected. It's all how you play with it.

Thanks for the comments. They've helped alot.

Kshatriya said:

You can also use the Imperials as an obstacle, something the Kill-team is forced to use their more social skills and talents on , rather than their bolters.

You can also use genestealer cults as a source of intrigue.

The 'nids can also be used to create unusual situations. DJSunhammer pointed out that you can use other Imperial factions as obstacles (even enemies!) in 'nid scenarios, but you can extend this even further. What if the Imperials aren't the only ones under attack? What if defeating the 'nids requires negotiating with Tau or chaos forces? Can the players swallow their hate and accomplish the mission?

A couple of plot seeds that might inspire a little:

*Defending a space port as Arbite and Guard personnel load civilians onto the last transport out.

*Hunting vanguard organisms through a Hive City paralysed with fear and rioting due to the incoming Nid invasion.

*Fighting through a hive ship to get to the brain in order to set explosives around its primary brain stem.

*Hunting and capturing genetically pure samples of tyranid creatures to develop a toxin to stop them.

*Raiding the ruins of a pre-imperial human world that is rumoured to have a weapon that destroys flesh on planetary levels.

*Going into a tyranid held continent to clear out a fallen fortress, reactivate the plasma generator and relight the void shields to create a beachhead for the counter invasion forces to land at.

*Destroy a new breed of tyranid that has been bred to ignore the presence of and obey the instructions of Tau Ethereals with bonus renown being awarded if the Tau are unaware of the Astartes intervention and are led to believe that their experiments in the area have failed.

*Guarding the precious geneseed of fallen Asartes as it is transported back to the Gate to be transported to their originating chapters. The tyranids are somehow aware of the potent cargo and have sent drone ships to reclaim it.

*Delivering tainted genetic samples to the heart of the Hive swarm. These samples have been tailor made to seem appealing to the hive mind but introduces a genetic weakness into the swarm, such as a lower tolerance to las weaponry or a weakness to a certain type of plague.

Hopefull some of those appeal.