Guida contratto / boss Morvudd in The Witcher 3 Wild Hunt [PS4 - Xbox One - PC]
The solution for this particular side mission of the game.
Guide Trophy / Objective "Devil or Demon?"
Morvudd's mission starts from the mission board in Rannvaig, a village on the main island of Skellige. From the bulletin board you will have to take the note "Contract: lost child".
The mission is fairly straightforward but it won't be easy at all. You will have to fight one of the strongest monsters in the game, Morvudd. The boss will kill you in 1-2 hits and is in pretty good health too, and since it will be necessary to defeat him twice in a row the recommended level for this mission is 30 and up.
The basic strategy for this fight is to dodge Morvudd's attacks by always throwing himself left, then use a single powerful attack and repeat. In this way you can proceed while continuing to circle around the enemy, with the right timing he will hardly be able to hit you. As already mentioned, his attacks are very powerful, so it is advisable to always have the Quen sign active otherwise you will risk being killed with a single hit.
After you defeat him, inspect his lair and then return to the man who gave you the mission to get the reward.
Here is a video showing how to complete this contract, good luck!