It is an easy fight on the first phase when he just protects himself behind his shield, i dont think there's a difficulty here, just avoid his smash, and hit him on the other side, that is all.
However, If you want an easy win against him when he starts to teleport & teleport & teleport, you just have to follow this pattern, especially on DM :
1) Face him, don't mark him/auto focus
2) when teleporting right behind you, roll (not dodge, ROLL) (before taking a hit of course)
3) reface him, stay at a correct distance and let him hit the air, then again, just roll forward when he teleports again
4) repeat until he smashes his mace into the ground, hit him ONE to TWO times MAX or you're dead because you'll miss and he'll be behind you again
5) repeat until dead
Teleport phase is very stressful when you discover the boss for the first time because it looks you can't do anything, especialy in DM where it's a one fail = dead but in fact, he always teleports right behind you.
However i dont really believe the few people who said "managed to beat him without problem on death march on first try", this is really impossible because the first time you discover his "SURPRISE TELEPORT !! O_O !" it's too late you're already dead, and even then, you dont know that there is only one moment where you can hit him, if you try to hit him in any other moment than when his mace is in the ground >> Dead ; and even when the mace is blocked in the ground, if you launch ONE hit when he suddently teleports back >> Dead