You must have killed Tairiza the Widow Mistress and collected an item from her if you want to have any chance at killing VS. Give the item from Tairiza to someone that isn't urgently needed when fighting VS.
Zone in to the main room. The hall directly in front of you will spawn 2 84x4 mobs once you cross the threshold between the main room and the hall. After these have been killed the position to which you pull Venril only matters to your preference. However, be aware, that VS has a couple AoE that are ranged base. If you can move more than 75 meters away from him before is AoE goes off you'll avoid it. The closer to him, the more damage it will do.The person who has looted the "item" off of Tazaria will spawn VS. To do this all they have to do is run into the room that the non-aggro VS resides. VS will not, or should not attack the person who ran into the room, instead he'll target someone else in the raid and head their direction. The person with the "item" needs to run behind where VS was standing and prepare to click on the two small figurines that start to glow every 10 to 15 seconds. If these two figurines are not disabled (right click, choose option), the statues standing in the hallway will spawn and kill you all.
Once VS is aggro the tank of course pulls him to a corner and Walk/Crawl. (VS has a fear shield that fears anyone who hits him 60% of the time. Curable) VS is a fight that everyone needs to pay attention to.
From the start of the fight he has 3 aoes that he will cast. The first one is shown to the right, Toxic infusion. This is cast approximately every 32 seconds (although it varies and is very hard to time). This needs to be cured asap. VS will then cast Fatalis 6 seconds later. If toxic infusion is still on the person when fatalis goes off it will explode their heart and ususally kill them instantly. If the person happens to survive the fatalis, it will still drain all their power, and spawn adds if you are further into the fight.
He also has a aoe stun that is cureable trauma. This trauma is much like the one that Pawbuster casts. Have your healers stand behind the dps, so that the DPS are hit with the trauma aoe. Healers can then cure.
Healers do not want to attack durring this fight (just heal/cure/debuff) because of the fear DS. If healer is feared durring toxic infusion it ususally means a wipe.
VS also has a spell reflect, it is minor it seems to be about 30% reflect..make sure your spell casters are aware. it does not seem to reflect melee or CAs, but it does reflect debuffs/spells/songs.
When his health gets to 65-63% he will activate his ring. Everyone with a cube from Tairiza the Widow Mistress needs to start clicking it. Have those people stop auto attack so they are not feared. Once the cube goes off it deactivates his ring and your raid can stop clicking the cube (much like overkings sword). If his ring is not deactivated, he will do massive consecutive aoes.
When VS get to 60% health he will start to watch your power, showing a green detriment uncurable icon in your detriment window and spawn adds for every person that has less than 25% power. He will nuke (small aoe range) anyone who has above 67% power, this nuke can be survived, but only if you have alot of hit points, and it can hit others near you.
He aslo casts a detrimental effect that looks like a purple icon in your detrimentals and it outlines your body in purple. It is uncurable, and everytime you use a CA/Spell/Heal/Cure you will use 225% more power to cast it. You do not want to cast anything while it is on you. This detrimental also increases your power by 1-2% per tick for 13-15 seconds, and then it reduces your power by 10% when it ends.
Few things to note: If you die you heal him 2-10% (most walkthroughs say 2% but we have experienced 10%). Use sprint to toggle your power, double clicking it will reduce your power by 15%, keeping it on and moving around will reduce it by 10% per tick after. Bards need to remove runspeed to use sprint. Sprint can be turned off while stunned but not feared, so turn off autoattack while toggling sprint to avoid being feared while sprinting.
Update change: Just keep power above 40%. The upper cap is removed.