This achievement is gained upon defeating the following rare monsters in The Plane of Hate:

Arcanist V`Gimis
Arch Lich T`Vaxok
Archon G`Uvin
an ashenbone broodmaster
Assassin Z`Jrix
Avatar of Abhorrence
Coercer T`Vala
Dread Knight T`Kamax
Dread Lord M`Noxin
an eerie chest
Evangelist W`Rixxus
a frightful chest
Grandmaster H`Qilm
Grim Abhorrent Kaltik
a grotesque rat
a hatebone broodlord
a hideous rat
Lord of Fury
Lord of Ire
Lord of Loathing
Magi P`Tasa
Master D`Samni
Master of Spite
Master of Vengeance
Master R`Tal
Mistress A`Zara
Mistress of Malevolence
Mistress of Scorn
Overlord R`Gahbsa
Sorcerer C`Gazin
Spy Master I`Kavin
Templar J`Rosix
thought destroyer
Vicar M`Kari
Warlock J`Rath
Warlord E`Prosio

Hidden Steps

• The Plane of Hate - Availability