This achievement is gained upon defeating the following rare monsters in Sverag, Stronghold of Rage.

Alchemist Darkfall
an imprisoned general
an imprisoned hero
Bedrock the Crusher
Breaktree the Giant
Broodwarder Heartknell
Builder Sneev
Captain Trevoz
Chief Star Eater
Chieftain Darkmaw
Clignak Poisoner
Crafter Ironpaw
Deathleap
Dewmane
Drogtar Deathmaker
Farsight the All Seeing
Firemane
Flamedancer
Fronk
General Vergomil
General Zerilijur
Gerind Weaponsmith
Gront
Gutslitter
Hivsgar the Terrible
Lord Zonz
Loreminder Brightmane
Master at Arms Prizenat
Mindbinder
Nightstrider
Pack Leader Bloodear
Prince Senifal
Queen Suvarla the Sterile
Restrained Cereton
Sendaro
Shaman Silktongue
Soulfury Embermeer
Svengor Goldfarb
The Skulltaker
The Subjugant
Tresvig Ravener
Vaslaghul Bonelord
Verzoo
Veteran Kerezal
Yoon the Gleener

Rewards

• Prefix: Rageslayer, Suffix: the Rageslayer