So this happened a week ago, I thought maybe it was just a coincidence.
But today again, exactly the same way.

In between I killed it as a group (much faster) and no issue.
It was when i solo it.
And always on convulsing in the exact same way.

wilderness subterranean <1057hp 595m 816mv 26000tnl (-24.40%) 10 AM>
You dodge the dark-elven transmuter's piercing venoms.
You get in one more shot on the dark-elven transmuter as he flees.
Your parting blow DISMEMBERS the dark-elven transmuter!
The dark-elven transmuter has fled!
The dark-elven transmuter leaves east.

wilderness subterranean <1057hp 595m 816mv 26000tnl (-24.40%) 10 AM> dash e under trans
A Mine Shaft on the Second Level


(Purple Aura) (Translucent) A rogue dark-elf slinks in the shadows.
You close into the dark-elven transmuter with some strong thrusts up under his ribs.
Your underhand strike DISMEMBERS the dark-elven transmuter!
Your underhand strike MASSACRES the dark-elven transmuter!
The dark-elven transmuter is convulsing on the ground.

wilderness subterranean <1057hp 595m 813mv 26000tnl (-24.40%) 10 AM>
The dark-elven transmuter utters the words, 'eugfjsh yrzgp'.
Your skin twists and splits under the dark-elven transmuter's magical assault!
The dark-elven transmuter's disruption EVISCERATES you!
You dodge the dark-elven transmuter's piercing venoms.
You fail to get in one more shot as the dark-elven transmuter flees.
The dark-elven transmuter has fled!
The dark-elven transmuter leaves west.

wilderness subterranean <1012hp 605m 840mv 26000tnl (-24.40%) 11 AM> dash w under trans
A Mine Shaft on the Second Level


(Purple Aura) (Translucent) A rogue dark-elf slinks in the shadows.
You close into the dark-elven transmuter with some strong thrusts up under his ribs.
Your underhand strike MASSACRES the dark-elven transmuter!
Your underhand strike DISMEMBERS the dark-elven transmuter!
The dark-elven transmuter is convulsing on the ground.

Connected to host 162.249.126.23605m 837mv 26000tnl (-24.40%) 11 AM>

Using shadow dagger, ghostly dagger.
I believe i dash underhand each time
Imperial offense
haste
stoneform
berserk