The narrative and victory/loss conditions are made from the perspective of the Space Marine rather than the Tyranids due to my lack of understanding of Tyranid psyche lol!
Outpost Station Halicon
Missions Used (all from 6th ed):
Purge the Alien
Big Guns Never Tire
The Emperor's Will
Chapter 1: Into the Breach
The Black Templars make entry into the Halicon via a breach in the lower decks and arrive using Drop Pod insertion.
Mission: The Emperor's Will
Synopsis: Your forces have made entry into the Halicon. You need to establish a beach head for further reinforcements to arrive.
Mission: Big Guns Never Tire
Synopsis: Having established a secure base, your forces reinforce the staging point with formidable weaponary.
Mission: The Scouring
Synopsis: Your forces may have failed to secure the staging point. But fortune favours the bold as your remaining forces use speed to secure remaining viable staging areas for the coming battles.
Chapter 2: The Jaws of Death
Mission: Purge the Alien
Synopsis: The alien menace is now fully aware of your presence. They come for your strike force in vengeful bloodthirsty waves of teeth and claw. Blunt their attack and make the enemy fear your might.
Mission: The Relic
Synopsis: Within the ship is an artifact of great power and of xenos origins. You must secure the artifact for you sense it will aid your cause.
Note: In the case of The Relic, maybe the artifact would really contribute to in-game usage. Like increased WS for the squad in possession of it, for example.
Synopsis: You have lost the artifact...for now. You will need to retreat to more defensive positions and secure supplies for your wounded. You also inadverdently stumble upon a monstrous evil.
Chapter 3: The Brood Mother
Mission: Purge the Alien (modified)
Synopsis: Your forces have discovered the source of this taint. The foul beating heart of the Voidscream. An immense beast, a Tyranid Dominatrix! You muster your forces for war! This is it. Purge the Alien!!
Note: The final battle is always expected to be a dramatic one. And its ok to add some interesting rules and creatures/ characters to reflect its conclusion.
Primary Objective: Slay the Brood Mother
Creation of a nice 'Boss Type' monster or leader at the end of the narrative should also be quite the treat. But care methinks must be taken not to overdo it. I have created my version of a Dominatrix just for laughs.
WS BS S T W I A Ld Sv
6 4 8 7 6 5 4 10 2+
Special Rules: Monstrous Creature, Rending Claws, Bio Acid, Rage, Fearless, Psyker, Synapse Creature, Implant Attack, Armored Shell, Shadow of the Warp.
Broodmother: Roll a D6 on Turn 3 onwards, on a 3+ the Dominatrix detaches herself from the birthing sac. She is now free to move, run or assault. When immobile, she can choose to spawn D6 Warriors every alternate turn. She can no longer spawn Warriors if detached from birthing sac.
Note: You can also add Special Rules into the narrative to give it that added challenge.
Tyranid Organisms able to Infiltrate or Outflank can do so on any terrain piece. They can also assault the turn they come into play if they pass an Initiative test.
As per the rule. Troop choices can be recycled. Coming in at random table edge next turn if destroyed in current turn.
Hope you have enjoyed the read ;)
Have a good weekend all!