Dead Man's Party - The Witcher 3 DLC Hearts of Stone Guide

After the Boss Fight: Toad Prince, Once you're back to Oxenfurt, you need to enter Shani's clinic and head upstairs to begin with the cutscene. Talk to Shani and accept the request to join her at the wedding(Dead Man's Party). This The Witcher 3 Hearts of Stone Guide will provide you details on how to complete the Dead Man's Party Quest.

You require Level 33 to deal with the Dead Man's Party. In the central chamber, once your are ambushed by those Wraiths, throw some Yrden to get rid of them quickly. Now Examine the tomb in the north-east of the chamber with the use of the Witcher Sense. Also, you need to equip the Censer and then spread incense in the marked areas, later ignite the votive as you return to the central room.  

Now you have to deal with a few ghosts which will spawn and destroyed before Vlod will appear. He will try to possess you and end up taking the spot as Shani's +1 for the nuptials. So after the cutscene, in the central chamber make use of the Aard on the broken wall and climb the hole to loot the corpse at the bottom and retrieve the key. On your way to the tunnel, few spiders will ambush you halfway and  Vlod will give you some grief.

You're unable to fast travel once your outside, so make use of the horse to get to the next marker. Here Vlod will possess you again and this time it will be a bit meet and greet including some distractions. The Pig wrangling should be a bit exercise in frustration or if you have a very strong Gwent deck to be destroyed by the Halflings. Eventually after all this diversions, you'll end up dancing with Shani where Gaunter will show up and bother you. 

Yet Another lengthy cutscene will begin and will trigger the Quest: A Midnight Clear. After this go and search for rowan bush and take her some berries and go through the dialogue option. Here if you show an interest it will lead you to a romance scene else it will end up normal and To finish Dead Man's Party quest make you return to Oxenfurt and speak to Olgeird.