Turias

Hello guys, im ensuring a strange problem against Maerwald. He is one shotting me nearly every time and if i dodge his strange Nuke he just can't die because everytime he get in low health ( near the death) he just instantly recover all his health. so what's going on? is that a filthy strange bug or am i just noob? how can i get srsl yone shotted or trolled so early in the game? EDIT : i actually tried from yesterday night to today during like 10 hours in all the ways possible. Explain/fix or Refund