Force: The Doom Harvesters (Warband)
Religion: Nurgle
Colours: Basic Colours.
Strength: ~100 Marines, Innumerable Zombies
Description: The Doom Harvesters firmly believe in the aspect of Entropy in Nurgle, and see it as their duty to break down all logical structures. Rejoicing in even petty destruction, the Harvesters are pyromaniacal at best, and outright genocidal at worst.
Characters:
Lord Pyros Deathwish
Lord Pyros is the Warlord of the Warband, and has absorbed the destroyer hive. Much like Typhus, he has been blessed with the ability to cause a zombie plague. Unlike Typhus, however, he uses his powers purely to destroy all semblance of structure or order in whatever he faces. Pyros wears Terminator armour and wields a large daemonically possessed poleaxe named Ishva'kar.

Force: The 293rd Landsharks (Human Military Regiment)
Religion: Be'lakor
Colours: Steel Legion Drab, Abaddon Black, Leadbelcher.
Strength: 5,000 men, fully mechanised. Unaccounted vehicle strength.
Description: The 293rd Landsharks are the 293rd military regiment raised on Kar'vahoth, and are fanatical followers of Be'lakor. A mechanised regiment, they are sent out to reinforce the Doom Harvesters and to lay siege to Imperial worlds.
Characters:

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Information:
"Upon the finalization of a regiment, the entire regiment must participate in a Bloodrend Ritual. During a Bloodrend, the regiment must be set upon a city of unarmed people (preferably Humans or Eldar), to murder them in extortionate numbers for 24 hours, after which, they must withdraw. The deaths must be dedicated to Be'lakor. At the end of each Bloodrend, the survivors must be taken to The Manifestation to be processed." - Military Doctrine of Kar'vahoth.

Force: An Ultramarine battle group of variable strengths.
Religion: Imperial Doctrine
Colours: Ultramarine Blue, Gold, White.
Strength: Variable.
Description: This particular Ultramarine battle group has been sent to destroy the Doom Harvesters. Many of the marines involved are experienced with dealing with Chaos.
Characters:
Captain Agemann, 1st Company Captain

Be'lakor
Be'lakor is the master of Kar'vahoth, and many other worlds. In the case of Kar'vahoth, he became worshipped as a god there by the majority of the planet. Their worship brings power to him, and he grants them gifts in return. He is known to partially manifest himself for them by allowing a modicum of his power to possess one of their number to act as a "guiding" force. He is capable of manifesting this power even when he would normally be unable to create a coherent manifestation of himself in the materium. Such a manifestation, however, requires specific and costly rituals.

Location: Kar'vahoth (Planet)
Segmentum:
Subsector:
Dominant Terrain: Daemonically-Infested Hive Cities and Toxic Wastes
Population: Roughly 9 Billion humans, excluding the sacrificial imports, Innumerable Daemons and Beasts.
Description: Once a hive world, now a daemon world, this planet was once part of the Imperium, but has since been claimed by Be'lakor, who has seen to it that this planet provides a military strength for him to command. There are several Hive Cities on the planet, each of which has become a mangled daemonic mess.
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Overview
Kar'vahoth is a mess of daemon cults, military factions, police-state-hive-cities, beastman tribes, rebel (Imperial) forces and toxic wastelands. Most humans on this planet worship the Daemon Prince Be'lakor. Day-to-day civilian life is much the same as you would expect on an Imperial world, except that there are no construction workers, as each city has a sentience of it's own - a culmination of many daemonic entities, and the souls of the dead - that controls the city's form.
The capitol is the Hive City "Avarice". Avarice is home to over 750 million humans, and at its -literal- heart is the technological monstrosity known as "The Manifestation".

The Manifestation
The Manifestation is a daemon engine capable of actually creating daemons. It is a construct that covers an area of roughly 3 sq kilometers, and rises another 3 kilometers into the air.
The Manifestation is a complicated network of summoning platforms, corpse furnaces, extra dimensional shapes and weapon forges. Every day, hundreds of sentient creatures are fed into the corpse furnaces or become incorporated into a ritual on the summoning platforms. Through occult sorcery, the souls of those slaughtered in The Manifestation are gathered to coalesce into new warp-based monstrosities, much like normal daemons. Unlike normal daemons, however, each of these are unaligned to any particular god, and are simply formed of the torment of mortals (like Furies). The importance of this is that none of them have any sort of allegiance, nor do they have much willpower. This means that the followers of Be'lakor can use them as fairly safe energy sources.
These daemons are known as Torments.

A typical use for a Torment is as a power supply for vehicle or weapon systems (such as in Chimera APC's or Lasguns). Rarer uses include supplying energy to a suit of power armour (which requires dozens of Torments) or even as spare psychic energy for a Psyker.

A Torment is sentient throughout it's existence, and becomes a malicious entity. Most Torments degrade, and will eventually fade into the warp, where their remaining energies will be consumed by true daemons. Some, however, may actually grow in strength and even be able to overpower their host/user. Such Torments may be placed into a daemon weapon.

[...]

(This was a 400 point kill-team match between the Doom Harvesters and the Ultramarines)
Night fell on Skarren IV with a sluggish pace.
Sergeant Merrik of the Doom Harvester's Warband marched fifteen of his brothers to the rendezvous point. They were to meet up with one of the warband's many psychically controlled zombie mobs, who had managed to take down a unit of Ultramarines who had been riding in a Rhino APC.
Lord Pyros had dispatched Merrik to retrieve the Rhino, and then to infiltrate the Ultramarine's territory and take out one of their outpost positions. The plan was for ten of his men to quietly roll up towards the position whilst outwardly looking like Ultramarines (to avoid giving any scouting forces cause for alarm) and wait for the other six marines to secure the area on foot. They would then close in on the outpost, quickly slaughter the scouts and marines inside, and leave as quickly as possible.

For the most part, Skarren IV was a fertile agri-world, but it does have its moments when the summer temperatures in some places soar above 70 degrees centigrade, generally killing off the population. The target outpost was an abandoned farm, the subject of a fairly recent "heat flash".

They marched for quite some time through grassy fields, which slowly gave way to barren dirt as they drew closer to the rendezvous.
Upon reaching their destination, Merrik saw how badly their plan was going to go. The zombie mob was far larger than expected, and had not only managed to kill the Ultramarines, they had also damaged the Rhino, and covered it in the early stages of Nurgle's rot. One track had broken off, the top hatch had caved in and the blue paintjob was almost entirely gone.
The upshot of this was that now there was no way in hell they were going to go in unnoticed. Looking over the nearby dead Ultramarines, Merrik saw that two of them had zombified. They hadn't deteriorated yet, and there was a nearby missile launcher.

This gave Merrik an idea.

Opening a mind-link between himself and the two zombies, he commanded one of them to get into the Rhino's driver's seat, and the other to pick up the launcher.
Turning to his men, Merrik commanded them "You six, Varron, Augthur and you with the plasmagun, get inside the Rhino, the rest of you will climb on the top of it!"
His unit consisted of fifteen brothers and himself armed primarily with boltguns, one of them had a plasmagun, another has a missile launcher and carried krak missiles. Merrik himself had a combi-bolter.
This new plan was going to be fun. Sending the missile-laden zombie to lock himself into one of the Rhino's fire hatches, he went over the new plan in his mind.
They would now all ride the Rhino as fast as possible up to the outpost, hoping nobody sent in reinforcements. Once at the outskirts, the six men on top of the Rhino would jump off, and move to flank the farm with the missile launcher. Merrik and nine of his men would stay in the Rhino and drive right into the heart of the outpost and start the killing. The missile zombie would provide fire support in tandem with the Rhino's stormbolter. Merrik made sure to reiterate this plan to all of his brothers.

Giving the driving zombie a command, they set off in the Rhino, speeding across the hardened dirt, pock-marked with impact craters.

It wasn't until they approached the farmland that Merrik realized they had been spotted. Just as he started to make out movement, they were suddenly subject to a hail of fire from several sniper positions from the wooden buildings that sat atop the very hill he'd hoped to gain some cover from.
Abandoning his original plan, Merrik commanded the marines on top of the rhino to make a break for cover at the base of the hill, and urged the driver to pick up the pace.
With a word to his plasmagun-wielding brother, they both aimed out of the ruined top hatch, Merrik scoring a kill with his combi-bolter. The plasmagun, however, was much less effective. Rather than spitting a ball of white hot plasma, it detonated, destroying the top half of the marine that wielded it. They were damn lucky it hadn't gone off inside the Rhino.
Taking a glance to his left as the Rhino started to climb uphill, he saw that the marine with the missile launcher had been taken out by sniper fire.

"What the hell do you think you're doing! Pick up that launcher now, you dumb bastards!" roared Merrik, as a round whizzed past his faceplate. But to no avail.
One of the remaining five marines turned around to pick up the launcher, but was promptly destroyed in a manner that Merrik hadn't seen for millennia.
With a sound like that of an angry god, the marine's power armour was crushed into a pulp by an unseen force. Grav guns.
That realization damn nearly had him calling for a retreat.

There were still four of his men running up the hill, and his Rhino, nine more men and himself (now breaching a wall of sandbags) still remained. Unless they had been spotted a particularly long way off, there wouldn't be many scouts here. And regardless of their armament, Merrik thought he would be able to take out a unit of ten, even by himself. Nine now, considering the kill he'd just made.

Jumping out of the Rhino, along with his men, they found themselves between two walls of sandbags with a small number of scouts inside. The encounter was swift and brutal, killing all in sight. But that hadn't lessened the incoming firepower. If anything, it had increased. Further up the hill, Merrik could see heavy bolter fire raining down shots upon them.
Sending a command to the missile-wielding zombie in the Rhino, he called for a missile to be sent at the emplacement up the hill.
Shrapnel flew for several feet in every direction. It had been a frag missile. If he had had any time, Merrik would have berated himself for not checking the zombie's ammunition stocks.
But, as it was, Merrik could see power armoured somethings charging out of another building. Space Marines. Battle hardened Ultramarines, who, judging by their armour's decor, were Sternguard.

With a Grav gun.

Now with his marines imploding around him, and still under sniper (and now bolter) fire, Merrik's nerve broke. There was nothing he could do. He looked for the Rhino. It was a burning wreck, and he hadn't even noticed it go down.

He ran for his life, sprinting across open terrain, praying to Nurgle that the enemy would fail to stop him. He would have to convey the bad news to Lord Pyros. And his failure hurt more than any mortal pain he could remember.