The Skaven are treacherous rat folk wich live in underground tunnels that stretch to every corner of the old world als known as the under-empire. They know no trust and prefer backstabbing instead of a fair fight. Every Skaven sees himself superior above all else, this means that the Skaven won't fight alongside any other race of the Warhammer world. The only thing that keeps the Skaven from mass slaughtering themselves is the Council of Thirteen
The council of thirteen contains 12 of the most powerful Skaven lords titled ''Lords of Decay''. The Horned Rat is figuratively the 13th member. The Skaven do not know loyalty only fear. Fear is the only thing that keeps them from betraying the council. Any Skaven stupid enough to do so will quickly be taken care off by one of the many Skaven assassins in the under-empire. The council gathers in the city of Skavenblight wich is the heart of the Skaven under-empire. Because Skaven really like fighting themselves huge ground assaults don't happen that often, the council is the only thing that can organize a Skaven army to attack what lies above them.

The Skaven do not know the words pity, remorse, compassion, or cooperation.
Only fear, kill, take, keep, survive and die.

sources: http://www.vermintide.com, http://vermintide.gamepedia.com/Vermintide_Wiki

All the races of the Old World have their distinct priorities and wants and needs. For the Skaven, both individually and as a faction, the lure of power is their sole drive and motivation. While the intricacies of Skaven psychology and society would require a lengthy essay or twelve, a basic knowledge of their verminous motivations will serve well enough for the layman or citizen desperately fighting for his home.
Among Skaven, Warpstone is the most coveted resource and commonly used as currency. Slaves, weapons and armour are other necessary tools in the scheming and brutal scramble for power that is the Skaven existence.

Unlike the Humans and Dwarfs, the Skaven masses see no inherent value in gold, and a lowly Clanrat would most probably ignore a coffer full of a treasure for some juicy meat, a rusty sword or the tiniest speck of warpstone.

Shrewd Skaven leaders with ambition and vision, however, see the value of gold and valuables as the means to influence and corrupt the greedy man-things of the surface world.

Among the Clawpacks of warrior vermin assaulting Ubersreik, there are reportedly Skaven agents carrying large sacks and seemingly acting independently from the invading force. They scour the town for valuables, most likely on orders from an enterprising chieftain or warlord, pouncing on the opportunity to expand their influence.

The lowest of the low in the Skaven hierarchy, Skavenslaves perform the most menial and/or dangerous tasks, and constantly face the threat of being devoured by their kin. In battle, they are deployed for meat grinder tactics, swarming the enemy in sheer numbers, and therefore lack armour and decent weapons.
The Skavenslaves will always attack in great numbers, either through a coordinated attack signalled by a battle horn, or through an ambush. If they manage to surround you, fight with righteous fury and pray to Sigmar you’ll live.

Tips, tricks and trivia for how to kill-kill a Skavenslave

The Clanrats make up the bulk of the Skaven army and are among the lowest ranking in the vile clan hierarchy. Slightly shorter than your average man, the Clanrats matted fur is filthy and patched, with wounds and boils covering parts of their body. They are clothed in rags and scrap armour, carrying worn down swords, knives, maces, flails, spears, and torches.
The Clanrats’ strength comes from their great numbers, surrounding and overwhelming their enemy by attacking from all directions. While banded together, the Clanrats bolster each other’s confidence and aggressiveness, encouraged by the screaming of orders like “kill the man-things, quick-quick”. Yet these warriors are cowardly at heart and lack basic discipline and determination, so if the odds turn against them, the remaining Clanrats will start to cower away or even flee the battle.

Tips, tricks and trivia for how to kill-kill a Clanrat

Wearing heavy armour, red cloth and a crest adorned helmet, the Stormvermin are among the fighting elite of the Skaven clans. Well trained in the use of halberds, they are tough challenge in one on one combat. Stormvermin will mix up stabs, swings, blocks and parries, to always keep the players on their toes.
The Stormvermin are often seen ordering the Clanrats around, shouting instructions and egging the rest of the army on, thereby bolstering their aggression. They are leaders in battle, and will not break and run as easily as the rest of their kind.

Tips, tricks and trivia for how to kill-kill a Stormvermin

Facing a lone Stormvermin can be quite a challenge, but taking on a whole Patrol is borderline suicidal. Using their tactical training, the Stormvermin Patrol will quickly surround individual heroes and with just a few well placed blows bring the player to their knees. If the Patrol is engaged, the players must work together and be constantly aware of their surroundings if they are to survive.
The Stormvermin Patrol are the only enemies in Vermintide that can be avoided, if you manage to sneak past them. While you may risk bumping into them later as they continue their patrol, avoiding them is oftentimes the safest and best bet. Accomplishing Mission Objectives is what will win the war, not suffering unnecessary casualties in pointless engagements.

Tips, tricks and trivia for how to kill-kill a Stormvermin Patrol

Packmasters are Clan Moulder troops tasked with driving packs of ravening beasts into battle, using whips and intimidation to spur their charges into a frenzy of teeth and claws. However, the Packmasters hired by Clan Fester in their assault on Ubersreik, are predominantly equipped with things-catchers, a pole arm designed to incapacitate opponents by strangulation.

It is still unknown why Clan Fester has paid the extra warpstone tokens for this somewhat unusual specialisation.
Without support from the rest of the group, the hero will face inevitable death when caught by a Packmaster. After catching his prey, the Moulder-kin will first try to put as much distance as possible between the captured hero and the rest of the team. When ready, the Packmaster will hoist the helpless victim into the air, and end the hero’s life through a gruesome hanging.

Tips, tricks and trivia for how to kill-kill a Packmaster

For a Gutter Runner, stealth is everything. Always moving in the shadows, the Gutter Runner wear a black cloak to blend in with their surroundings and make as little noise as possible. Equipped with Warpstone Rat Claws that glow a sickening shade of green, the Gutter Runner will expertly leap at its enemy, using its weight and momentum to knock the player onto their back. Left prone and vulnerable, the Gutter Runner will then proceed to hack into the hero’s torso, forcing the rest of the players to rush to the aid of their comrade.
Having undergone gruelling training in their mysterious fighting styles, the Gutter Runner is able to bend and contort its body, making it incredibly nimble and able to move at speeds unachievable by man. While attacking a hero, it will focus all of its attention on killing them, but once the other players start attack it, the Gutter Runner will roll backwards and disappear into a cloud of smoke.

Tips, tricks and trivia for how to kill-kill a Gutter Runner

Wearing their signature robes and gas mask and carrying a heavy rebreathing apparatus, the Poison Wind Globadiers have actually strapped a ticking time bomb on their backs, since the container is filled with highly combustible warp-gas. These hired elite soldiers can be heard from quite a distance, clanking and wheezing their way into battle, whilst preparing their globes with deadly green gas to be flung at their enemy.
Upon impact, the globe shatters and spreads the toxic fumes, dazing and damaging any who might be caught in the resulting cloud. Life is cheap in the eyes of the Skaven, and the Globadier does not care if Clanrats are caught within the cloud along with the targeted enemy.

If our heroes manage to cause heavy damage to the Globadier, it will go into a frenzy as its apparatus has been breached and becomes unstable. The Globadier will then charge the players in a suicidal attempt to take them out. If they don’t manage to kill it in time, the Globadier and his equipment will explode in their midst.

Tips, tricks and trivia for how to kill-kill a Poison Wind Globadier

The Ratling Gun is a six-barreled monstrosity of a gun, powered by warp steam and operated with a hand crank. This fearsome weapon of unparalleled rate of fire is normally operated by a Clan Skryre weapons team, but the version deployed in Ubersreik seems to be of a lighter, experimental type, capable of being moved and fired by a single Skaven.

Encumbered by the weight and unwieldiness of the weapon, the Ratling Gunner is far from quick on his feet, but once he cranks up his weapon and opens fire, warpstone laced hell is unleashed. Single minded and persistent, the Ratling Gunner will pick a target, and then continually track it, firing relentlessly until either the weapon jams, needs to reload or the Hero lays dead and shredded beyond recognition.
Much like his colleague the Poison Wind Globadier, the Ratling Gunner won’t let a small fact like Clanrats or Skavenslaves blocking his line of fire stop him. If a Hero can keep her wits about her (or him), the Hero can make the Ratling Gunner mow down his kin, whilst dodging from cover to cover. However, be sure to not get caught in the open, or face a rapid fire death in a hail of warpstone gunfire.

Tips, tricks and trivia for how to kill-kill a Ratling Gunner

About twice the size of a regular human, the Rat Ogre is the result of horrendous surgical and crossbreeding experiments (mainly, but not limited to, between Skaven and Ogres). A feral, primal nearly unstoppable killing machine, the Rat Ogre has the strength and size to cause the ground to shake as it charges. Should our heroes fail to move and be caught in the charge, they’ll find themselves on the receiving end of the Rat Ogres claws.

The Rat Ogre is also known to grab nearby victims (like a hero, for instance) and throw it quite a distance. For the hero, sailing through the air might be exhilarating, but the abrupt and painful landing is definitely not.
On the whole, the Rat Ogre is a mindless brute, relying on aggression and muscle to get the job done. It will focus its attacks on one hero at a time, enabling the rest of the party to assist in taking it down, while the Rat Ogre’s attention is focused on its sole target. As always, the key to victory is teamwork.

Tips, tricks and trivia for how to kill-kill a Rat Ogre