You've defeated 100 cold demons, making you Coldhearted.
How to Get
Defeat 100 Circle of Thorns cold demons, including Hordlings and Hellfrosts.
Note: The badge completion bar will state that you need to 'Defeat the cold demons on Thorn Isle [A subzone in the northeast of Nerva] to earn this badge.' This is wrong, Nerva Spectral Daemons do NOT count for the badge, and hordelings and hellfrosts only appear in lower level areas. Hellfrosts can easily be found along the coastline around Plotter's Field in Sharkeshead Isle.
Gladiator Badge Unlocked
When you obtain this badge, you will unlock the Hellfrost Gladiator badge.
This badge is required to unlock the Demonic Badge accolade.