Guida contratto / boss Therazane in The Witcher 3 Wild Hunt [PS4 - Xbox One - PC]
The solution for this particular side mission of the game.
Trophy Guide / "Ash to Ash" Objective
The Therazane mission starts from the mission bulletin board in Hierarch Square in Novigrad. From the bulletin board you will need to take the note "Contract: haunted house".
Go to the inn near the quest board and talk to the man upstairs who will send you to a mansion in Novigrad. Enter the cellar to get acquainted with Therazane, a powerful Boss that an incredible amount of health and very powerful attacks that can kill you with just 2 hits.
To win against Therazane you must first of all keep in mind that it is resistant to almost everything, therefore always keep the Quen sign active. The basic strategy is to attack Therazane with 1-2 powerful attacks, then immediately dodge backwards to evade her blows. Once you learn his attack pattern it will become easier, also because he is a very slow enemy with powerful but easily dodged attacks.
Remember that by attacking him too many times in a row the boss will go into a defensive position, be careful not to attack him when he does this because it will be able to block the attack by causing a massive explosion that could kill you instantly.
Here is a video showing how to complete this contract, good luck!