So... My players will go come across a zeno artefact that contains a map - among other things - and will go out hunting various interesting items they can see on the map... One of them is - I have not yet decided exactly what it is, possible a C'tan shard - happens to be located on a necron crownworld that are awaked and have largely mobilised its forces... The players are aware that the necrons are active in the area and initially i figured they they would leave the the world alone.. But recently i came to worry that they might decide to be bold (read arrogant) and jump their fleet out and try to grab the item... I hope they turn tail once they ram their head into the necron fleet that is waiting... However the Necrons are going to retaliate, the Question is: How?

My players are well-equiped, they are almost an extention of the AdMec, and they are badasses in their own right, and have power and influence, but this is beyond their power...

Show them what's up, and if they persist, kill them. This is one of the many things that fate points are for.

Have the Necrons already kicking the butt of a superior force.

Perhaps a previous antagonist? Eldar or Orks? They jump in and they see a massive xenos fleet getting its ass whooped by the Necrons, and they can nope out of there.

I agree. Though I wouldn't have another enemy fleet be there, because that would be a prime distraction. Maybe the remains of many a fleets. A good idea is to have most of their NPC ships get shredded to peices in a few short rounds, while their ship gets pummeled. If they don't get the hint, then have like 10 enemy ships converge of their one ship should. If not, then like Magellan said, they have fate points for a reason.

Brilliant ideas! Thanks guys

Have the Necrons already kicking the butt of a superior force.

Perhaps a previous antagonist? Eldar or Orks? They jump in and they see a massive xenos fleet getting its ass whooped by the Necrons, and they can nope out of there.

As Marwynn said. Nothing strikes fear like seeing a close rival getting torn into like afat kids first happy meal of the day.

1. Give the characters a map to the treasure, marked with an "X."

2. Put a dragon on top of the "X."

3. When characters arrive they see the dragon.

4. Characters die.

And fun was had by all.

1. Give the characters a map to the treasure, marked with an "X."

2. Put a dragon on top of the "X."

3. When characters arrive they see the dragon.

4. Characters die.

And fun was had by all.

I would modify your rules as follow

3) Before characters arrive, the dragon sees them.