The following elements are key elements of the Dungeon
Ice Chi
The ice chi is an arcane orb, 4 inches in diameter, that acts as a catalyst for the growth of everice. It can be used as an arcane focus. If you use it to cast a spell that deals cold damage, you can reroll the damage dice and use either result.
Construction and Environment
Unless otherwise specified, the walls, floors, and ceilings of the catacomb are worked masonry. The walls and ceiling are covered with a 1-inch layer of ice. Doors are stone; stuck stone doors require a DC 15 Strength check to open. The whole catacomb is underground and in pitch darkness.
The temperature is around zero degrees centigrade: if the party wishes to take a long rest anywhere they must have winter blankets or some means of creating fire. However, a fire will melt a room’s ceiling ice after four hours, foiling a rest attempt unless the party took precautions against water.
Ecology
The halls and corridors of the catacomb are normally mostly devoid of life. A breed of rodent, the giant ice rat, sometimes finds their way into the dungeon through cracks in the ice to feed on vermin. More recently, some members of the cold legion have been freed from their ice-block prison and they patrol the catacomb while they wait for their comrades to thaw.
Surrounding and Entrance
The area above the catacomb is a featureless field of snow banks, with the occasional outcropping of rock. If the PCs take the time (1 hour) to investigate the area, they may find the grill leading to the secret room (30). This requires a successful DC 20 Investigation check.
Timeline
Cold legion creatures are resurrected at midnight. You should note where they have been slain, and keep track of the time of day as the party explore and take rests.
48 hours after the start of the adventure, the ice imprisoning the cold legion finally breaks and the following creatures appear:
- Room 7: 4d20 cold legion minions; 4 cold legion slingers
- Room 13: 1 cold legion veteran
- Room 18: 4 cold legion minions
- Room 27: 4 + 1d6 cold legion minions
The thawed prisoners will spend 1 hour consolidating, and then make their way to the exit (emerging in a single file) to wreak havoc once more. How many prisoners are frozen, how many get unfrozen, and what cold legion creatures these prisoners are, are choices left for the DM.
Rewards
Since cold legion creatures can rise after being slain, only award XP for defeating them the first time.
If the players refreeze the catacomb and escape, award 450 XP (divided among the PCs). They will also have the gratitude of the dwarves of Nalrim
Random Events and Encounters
Each time the party enters a location, roll 1d20.
According to the results, here’s what can happen:
- 1–10: No event
- 11–12: 1d4 ice rats
- 13–14: 1d4 cold legion minions
- 14–16: A chunk of ice falls from the ceiling. Select one creature in the room at random. They must make a DC 11 Dexterity saving throw. On a fail, they take 1d10 bludgeoning damage.
- 17–18: The party come across a small brass mechanism. It is a part of the buckler guardian at location 17. If all five are found, ignore this random event result.
- 19–20: The faltering power of the frozen pool courses through the location. Creatures with cold resistance or immunity are restrained for 1 minute.