An immense centipede-like beast erupts from the snow, rows of chitinous plates on its back glowing red-hot.
Source: Dungeons & Dragons Monster Manual 5th Edition
Living in glaciers or the tundra of the north. Laying silent in their carved out warrens created by their intense heat the Remorhaz wait. A sudden vibration in the snow and ice above springs this creature into action. With a sudden explosion of ice beneath your feet this fearsome arctic predators burst forth from the ground. With one intent to have you as dinner.
Remorhaz are found in arctic climate. Generally feeding on local prey like elk and polar bears. Their bodies generate intense heat that let's them create mazes of tunnels beneath the ice and snow. When waiting for prey they can lower their body temperature so it doesn't melt it's cover. They are cunning predator with low intelligence but can understand the giant tongue and at times controlled by the local frost giant tribes.
Remorhaz are huge creatures. Typically being 25 feet long and weighing 10,000 pounds. This mid-level challenge employ a vicious bite and ability to eat their prey whole.
Combat: Remorhaz is a huge monstrosity with a challenge rating of 11.
-Movement: 30ft, Burrow 20ft
-Damage Immunities: Cold & Fire
-Senses: Darkvision 60ft, Tremorsense 60ft, and a Passive Perception of 10.
-Bite: +11 to bite with a 10ft reach. If hit by a bite attack the victim takes 6d10+7 points of damage plus 3d6 of fire damage. If a target is hit it is grappled. A DC 17 escape check to get out.
-Swallow Whole: The Remorhaz can make a bite attempt at the victim it is grappling. If the attack hits the victim takes the bite damage and is swallowed whole. While swallowed the victim is blinded and restrained. While inside the Remorhaz the victim takes 6d6 acid damage at the start of each of the Remorhaz turns. If the Remorhaz takes 30 or more damage on a single turn from inside it's body it must make a DC 15 Constitution saving throw or regurgitate the contents of it's stomach.
The Remorhaz makes for a great random encounter while travelling through an arctic climate. They are the perfect ambush predator. With a massive amount of damage from their bite attack and the ability to eat your players characters whole makes an encounter with a Remorhaz quite deadly. Add in environmental hazard of the frigid cold and you can have a perilous situation on your hands.