First, a little bit of history about my character...

Cornelius Savo was a promising Commissar in the Imperial Guard. He was a bit different from most Commissars though. While firm with the discipline as most Commissars are, Savo had a knack for inspiring his men through non-physical means as well. He also showed some smarts in the arena of tactics and overall command. His popularity began to worry his superiors so in a bold move they decided to remove him from the Commisar corps and instead send him off to the depths of space with a Rogue Trader Warrant. Spun to be a promotion Savo agreed (but of course knew what was really happening) and went forth with this new endeavor on behalf of the God-Emperor.

So now he has amassed a ridiculous amount of wealth and a fleet of ships including two cruisers and his own ship-building facilities. He even managed to do almost all of this during an active Crusade (That he called) against the Necrons in his area of operations. He has numerous planets that are under his control, he has his own military troops (several regiments now with more having been gifted to the Crusade). He even has a vid-cast show that transmits his exploits all over the systems in his influence (he has become quite the celebrity).

The problem is this...

We are losing the war with the Necrons. We are losing badly and if we don't turn the tide soon all will be lost. It has come to the point to where Savo himself is leading an expedition into the Koronus expanse to find something (weapon, ally, ANYTHING) that will turn the tide.

What should we be looking for.

If memory serves me correctly, in the RT setting the Necrons are not out and about yet in the Warhammer 40k universe. However, in 40k, anything is canon, so below are some possible ideas

1. An item / device created by the C'Tan / Slann / Old Ones / Yu'vath / other unknown xeno race that disables the Necron ability to regenerate.

2. A weapon created by above xeno's that sucks out the Necron's "soul," however, is has the unintended consequence of converting this power to somewhere / something else.

3. Convincing an Ork armada to attack the Necron's main force because "it wud be ah good FIGHT!"

4. Gaining technology / weapons from Zayth / Naduesh / other planet with abundance of archeotech to assist in the fight against the Necrons.

5. Somehow convince the Kroots of a Warsphere that the Necrons actually wear armour, and underneath it is their skin; however, if you let them escape into the "green flash of light," you have to kill another one to try again.

A combination of what you and I mentioned above, in any order, or lack thereof.

"If memory serves me correctly, in the RT setting the Necrons are not out and about yet in the Warhammer 40k universe. However, in 40k, anything is canon, so below are some possible ideas"

Basically we are way out on the fringe and this may in fact be the first encounters the Imperium have had with the Necrons.

2. A weapon created by above xeno's that sucks out the Necron's "soul," however, is has the unintended consequence of converting this power to somewhere / something else.

I believe there's some stryxis tech, grenades and pistols called aetherflare if memory serves, that attack the soul so to speak, ignoring armor and such and leaving no visible wounds but injuring and killing anyway. Might be a possibility.

Found em. Aetherflare Grenades. Hostile Acquisitions pg 52. Might not work depending on how your GM rules it, but worth a try. Also the whip like Aetherlash on page 56.

The problem with exotic weapons like that is getting your hands on enough to fight a war.

I am of course going to bring up possibility of making a pact with the gods of the warp, because that would certainly solve the issue....if you don't mind setting a few worlds aflame as proper sacrifice. Maybe a grant of....uncommon luck among your armies, blame on the emperor if it makes you feel better. Maybe an increase in naval strength, and crush them from orbit. Maybe....maybe enlist the armies of the true gods, and allow them to show you the power of the warp made manifest in its chosen. There are plenty of deals one can make. Name your desire and it can be yours.....

That said, I think a genuinely good idea is to pop over to undred undred teef and drop hints about how incredibly effing awesome it would be to lay waste to Necron tomb worlds and all dem shiny bitz!! And then find the mercurial Eldar and convince them that helping you take out THEIR mortal enemy will benefit them greatly. Of course that's about as safe as my previously mentioned dark pact.

Politics.

You need to convince the Administorum to send more equipment! Convince the Navy to send more ships! Convince a Space Marine Chapter Master to send a company! If this takes finding something in the Expanse to threaten or bribe them with, than so be it.

It's always possible to find a Dues Ex Machina in the Expanse. Perhaps some relic from the War in Heaven. Will probably only work once, and require you to do something ridiculously epic to activate it. (like attach it to the High Necron Lord before pressing the button). Stargate, Reality Dysfunction, Mass Effect - these kinds of victory-Mechina are common in Sci-Fi works and may give you some ideas. Depending on how hands-off your GM is to, they might have an idea/plot/plan.

As a matter of fact, yeah! Bring the threat before the Angels of Death, and see their reactions. I betcha they would rush in with a couple companies just to say they had the honor of being the first chapter to give them a proper Imperial welcome.

Well, there are alrady two Space Marine Chapters here fighting in the Crusade. There is also a whole Imperial Battle-fleet and a small army of Inquisitors.

It is now believed that we have discovered two Tomb Worlds.

Well, there are alrady two Space Marine Chapters here fighting in the Crusade. There is also a whole Imperial Battle-fleet and a small army of Inquisitors.

It is now believed that we have discovered two Tomb Worlds.

Oh. OOOHHHHHHH. Um....is Chaos still an option????

EDIT: what about Exterminatus?? We haven't had a good old-fashioned exterminatus for a while, right?

There are many answers. This should be obvious from all the above possibilities. You have left out key information. Why are the Necrons beating you so badly?

Do they outnumber you? Is their mobility such that you don't know where they'll strike next? Can your troops not damage a standard Necron warrior? Do they have a fleet? Is their fleet destroying yours?

The questions are almost endless. Perhaps more details would help people help you.

I'm getting more intelligence tonight and I'll report back. I'm not sure how much info the GM is going to give us outside of what the characters know.

We also don't know anything about your GM, which is arguably just as important. Do you have a "Hands Off" GM that's doesn't believe in plots and is clockworking a sandbox, or do you have a "Storyteller" GM that works in the direction of a black-library style epic? Or something inbetween? What you're likely to find and have work depends as much on this as the actual threat.

He is something in between. He definitely has things going on behind the scenes (like some traitor Marines assassinated the first Lord Marshal) but he also gives us a very long leash with which to hang ourselves if we choose to.

From the GM:

There are a lot of reasons the Crusade is losing:

The Imperium doesn't know how to fight Necrons yet.

This is a tiny Crusade, not something huge like the Sabbat Worlds Crusade.

They definitely outgun you. Now at the Bale Embers they also outnumber you.

So far, you really haven't seen a "typical" Tomb World. Upsilon Beta is more like a border garrison. Xiu Delta was mostly Crypteks - lots of weird superscience. The Bale Ember worlds are something bigger than Tomb Worlds, and easily rolled over the Crusade's strike force, which was really only a few cruisers and frigates.

Basically, the Crusade got cocky and bit off more than it could handle.

My recommendation for you for dealing with the Bale Embers at this point in time is to destroy the planet and everything on it.

You're outgunned, out numbered and facing an almost deathless xeno enemy that has much more dangerous tech then you. While you might be able to find things out in the Koronus expanse that will change the tide of the crusade in your favor, that will take time and if what you're saying is true then the forces that make up the crusade will be destroyed long before you get back if they keep fighting the Necrons as is. Since most of the Necrons are on Bale Embers, then logically destroying Bale Embers will if nothing else buy time for you to go off and do your thing while the crusade can try and rally against the remaining planets.

Someone already mentioned the Astartes. Has your crusade encountered any Eldar yet? If so, Tell them about the Necrons. The Eldar view the Necron as the "Great enemy" and would not hesitate to ally with humans to defeat them. Let's not be too trusting though, The Eldar would happily sacrifice entire human worlds if they thought it would give them a shot at defeating the Necron or just preserving Eldar lives!

Or, find Eldar bases, maiden worlds, or a craftworld and leave that information where the Necrons can find it. Then, instead of waiting for the Eldar to offer you an alliance, offer them one. Let them play the part of the sacrificial lamb. The Eldar aren't the only ones that can play that game.

The Imperium hasn't had confirmed contact with the Necrons yet. All that means is your expedition is doomed to failure and vanish into obscurity. Optimism!

The problem with asking the Eldar for help is you shouldn't know that the Eldar will defeat the Necrons, and they will definitely only do so to screw over humanity. The problem with "help" for the Necrons is they're easily the most powerful thing in 40K and their only real weakness is there isn't a lot of them.

Try finding a non-organic Xenos race and throw them at the Necrons just as an experiment. They might not consider silicate based life as worthy of extermination .They probably would though.

Nameless2all has provided a pretty good list, but you could also make a pact with Tzeentch to alter your fate so that you never woke up the Necrons. Surely selling your soul would be a small price to pay to make sure these Xenos never awaken.

I have a sneaky suspicion that the tomb worlds, or at least the key structures, might be protected by the the Null Pillars, those things threat exist on Cadia, and fiddle with the warp, that many believe were of Necron origin. While I won't win an argument by saying "if Tzeentch COULD, then he would," there should be little to know reason (that I can fathom; he's weird, though) the Changer of Ways would want them to return, nd we know that the Necrons do, eventually. Pariahs might've gotten ret-conned out of the material, but I believe the pillars are still on Cadia, and I can see the Crons wanting to shield themselves from the warp, since there is little else they can do with it.

Wait, When did Pariah's get Retconned? They were in the last Codex I had! (5th ed.). I hadn't seen a replacement yet.

The most recent codex I had seen dropped them, I thought, and they are not available models, anymore. 2011 sounded their death knell. Once the C'Tan stopped being masters, and started being long-conquered tools, and the Necrons gained personality, Pariahs went poof, to the best of my knowledge. They've also not been referenced in the DW books, while almost everything else has. I have them in my smaller tomb world, if I ever do DW, but they are nothing official

I've seen the great, cheesy stat up Culexus Assassins get, now, however, and their mechanics are rather cool. I'm hoping that, if/when Necrons get a 7th ed codex, the Pariahs return, in a nifty way to give the Crons some anti-psyker power, as they have little else to do in that phase. Hoped Dark Eldar would get something, too, but it sounds like they sort of didn't, and Tau, I have no idea what they would ever have. Pariahs, though, could be cool again, and give the Necrons some oomph, even if they don't maybe need it.

The problem is getting to the point where my Rogue Trader would know that the Eldar are an option. What we are in the process of doing is we have headed over to the Koronus expanse and found a heretical Adeptus Mechanicus sect that has sent us to retrieve an item they believe will be effective against the Necrons. We are in the process of retrieving said weapon.

Meanwhile we have discovered through our spy network (because the Crusade has not been very forthcoming with information even though it was my character that called the Crusade in the first place) that they are engaged with multiple Tomb Worlds and one of them is actually the home of a Necron Guildhouse.

Dark Pact to improve your troops. Necrons struggle to get back up when put down by your troops fire, power flows less reliably, causing issues such as miss fire temporary loss of controle etc.

Throw some Exterminous Torpedos at any planet you find them on.

Leave and never come back.

Capture one and take it to the Mechanicus. I advise transporting, even a Warrior, on a ship you wont miss should it be destroyed and dont hang around the Mechanicus planet longer than you have too, just in case.
Let them come up with an answer.

Remember to invest in some stasis field gear if you intend to take any necrons or necron equipment back. Nothing else will prevent it from phasing out.

Exterminatus is perfectly viable.....failing that ( fethin optimistic inquisitor! ) You could always try to aquire some good quality nukes and ( using actual science ) detonate them near the systems sun(s) at the right time/angle to disrupt their magnetic field and unleash some intense solar flares that could easily strip the planets of their surface life ( and potentially atmospheres )..pretty hard to come back from a good solar cooking It would leave the planets largely intact for any available resources ( all be it a bit more "radiant" than they were before...but..meh....

Just make sure none of your side are on that side of the system when it happens.

(EDIT: I had a Player decide to do just that on me..it took him some seriously penalized tech rolls ( just to come up with the idea ) and a large expenditure in time and PF to locate and acquire the materials to create a shielded nuke laden torpedo set (he still had an epic fail on the delivery rolling a 97 to put them on target...used a fatepoint and then rolled a 98...I checked for how badly it went and rolled a 00...MASSIVE solar flares cooked both the planets in the inner cauldron....the remaining 4 planets in primary biosphere were slammed ( closest 2 in were stripped of their atmospheres--burned off , and the last two had a serious radiation burn and temp increase ( microwaved on high for an hour ) All in all...EPIC FAIL. But the premise is sound and could work if youve got better luck at dice...lol