Cryovain Menace of Icespire Peak

Cryovain’s Lair

 Cryvain's Lair is the carved innards of Icespire Peak surrounded by a slew of secret tunnels, held up by massive pillars of ice, jagged stalactites, a horde mimic, and an underwater lake of freezing water with slippery ice bergs floating within.

the entire area is considered difficult terrain and Extreme cold

A creature traversing slick ice at more than half speed is required to make a DC 15 Acrobatic check at the start of the movement. Failure causes the creature to fall prone at the start of the movement. Dashing on slick ice increases the DC by 5, with the same effect on a failed skill check. 

A creature that falls into freezing water, the must make a DC 13 Con save or be stunned for 1 round and take 2d6 cold damage half of a successful save, this save is remade at the end of each of that creature's turns that they remain in the freezing water

Lair Actions

On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects; the dragon can’t use the same effect two rounds in a row:

• Freezing fog fills a 20-foot-radius sphere centered on a point the dragon can see within 120 feet of it. The fog spreads around corners, and its area is heavily obscured. Each creature in the fog when it appears must make a DC 10 Constitution saving throw, taking 10 (3d6) cold damage on a failed save, or half as much damage on a successful one. A creature that ends its turn in the fog takes 10 (3d6) cold damage. A wind of at least 20 miles per hour disperses the fog. The fog otherwise lasts until the dragon uses this lair action again or until the dragon dies.
• Jagged ice shards fall from the ceiling, striking up to three creatures underneath that the dragon can see within 120 feet of it. The dragon makes one ranged attack roll (+7 to hit) against each target. On a hit, the target takes 10 (3d6) piercing damage.
• Blinding Sleet. Driving sleet falls in a 40-foot-high, 20-foot-radius cylinder centered on a point the dragon can see within 120 feet of it. Each creature in that area must succeed on a DC 15 Constitution saving throw or be blinded until initiative count 20 on the next round.

Regional Effects

The region containing a legendary white dragon’s lair is warped by the dragon’s magic, which creates the following effects:

• Chilly fog lightly obscures the land within 6 miles of the dragon’s lair.
• Freezing precipitation falls within 6 miles of the dragon’s lair, sometimes forming blizzard conditions when the dragon is at rest.
• Extreme Cold
• Icy walls block off areas in the dragon’s lair. Each wall is 6 inches thick, and a 10-foot section has AC 5, 15 hit points, vulnerability to fire damage, and immunity to acid, cold, necrotic, poison, and psychic damage.
  If the dragon wishes to move through a wall, it can do so without slowing down. The portion of the wall the dragon moves through is destroyed

• Avalanche If a creature fails a stealth check DC 7,  takes a fast pace up the mountain, or use an ability that creates a loud sound an avalanche will occur, up to once a day, the avalanche takes initiative count 20 and 10 lasting 2d4+4 rounds

  • Active elements

    Crush of Snow (Initiative count 20) A wave of snow beats upon the party. All characters must make a DC16 strength saving throw or be covered by a wave of snow. Creatures with a burrow or swim speed have advantage on this saving throw. Creatures that fail take 2d10 bludgeoning damage and are buried in one layer of snow and are blinded. If already buried a layer of snow, the save is made at disadvantage and if successful a creature is freed from 1 layer of snow.

    Tide of Powder (initiative count 10) Creatures that are buried in snow must make a DC10 Constitution saving throw. The DC for this save increases by 2 for each layer of snow under which they are buried. On a failure a creature takes 2d6 cold damage per level of snow above them half as much on a successful one.

    Constant effects The area within the avalanche is heavily obscured by a flurry of snow. This lasts until the avalanche subsides. Movement in the midst of the avalanche follows all the rules for swimming at 1/2 speed.

    Countermeasures a suffocating buried creature cannot shout and thus a DC15 perception check can be attempted as a free action to locate them.

    Grab onto something A creature that is not buried can use its action to grab onto a tree or rock, or find a safe outcropping. The creature attempts a DC15 athletics or acrobatics check. On a success the creature has advantage against the next saving throw against the Crush of Snow effect. If they succeed by 5 or more they automatically succeed on that saving throw. On a success, the creature is not carried down the mountain with the avalanche, and may become separated from the party. Creatures with a climb speed have advantage on this check.

    Digging yourself out A buried creature can use its action to attempt a DC20 strength check to dig upwards out of one layer of snow. If they succeed by more than 5 they dig out of two layers, if more than 10, three layers. Creatures that attempt this and fail while suffocating take one level of exhaustion. Creatures with a burrow or swim speed have advantage on this check.

    Dig out someone else A creature that is not buried can use its action to attempt to dig out another creature. The creature makes a DC15 athletics check to do this. The DC increases by 2 for each additional layer beyond the first that is on top of the buried target. On a success the buried creature is no longer buried. A character must be within 5 feet of their target to attempt this action. Creatures with a burrow speed have advantage on this check.

    Other clever actions some magical effects or items, especially ones that manipulate water, can be useful in this situation. Allow players making creative attempts leeway towards success. Anything that would aid in a situation where the party is swimming is likely to be of help here as well.

If the dragon dies, the fog and precipitation fade within 1 day. The ice walls melt over the course of 1d10 days