Colgera

Weak Point. The colgera has three weak points, one of each of its segments, that is protected on its back and exposed on its belly. Each belly weak point has full cover when attacked from the colgera's back, and half cover from the sides. When the colgera uses its multiattack, one weak point of the colgera's choice on its back becomes exposed. Only one weak point at a time can be exposed on the colgera's back. Whenever the colgera takes damage that is not targeted at an exposed weak point, that damage is reduced to 1 after applying any damage modifiers including critical hits. A creature that knows of the weak points (DC 15 Investigation or Nature check) can choose to target one if it is exposed: on a hit, the attack deals damage normally. When a segment is reduced to 0 hit points, the weak point is destroyed. When all three segments are reduced to 0 hit points, the colgera dies. Destroyed weak points regenerate with full health when the colgera finishes a short or long rest.

Colgera's Lair

On initiative count 20, the colgera can invoke ambient magic to take one of the following lair actions.

Gust of Wind. A 10-foot wide line of wind up to 60 feet long forms between two points the colgera can see within its lair. The wind moves from one end of the line to the other in a direction the colgera chooses. Ranged attacks that pass through the line are made at disadvantage. A creature that enters the line for the first time on a turn, or start their turn there, must succeed on a DC 18 Strength saving throw or be pushed up to 15 feet in the direction of the wind; if it rolls a 9 or less on its saving throw, it is also knocked prone. When moving upwind, each foot moved costs 2 feet of movement; when moving downwind, you move 2 feet for every foot of movement spent. The line lasts until initiative count 20 of the next round, or until the colgera dies.

Hail Storm. Massive hail falls in a 20-foot radius, 40-foot high cylinder centered on a point the colgera can see within 120 feet of it. Each creature in the cylinder must make a DC 18 Dexterity saving throw, taking 10 (3d6) cold damage on a failed save or half as much damage on a successful one. If the cylinder is touching the ground, the area becomes difficult terrain until initiative count 20 of the next round.

Seizing Mist. Freezing fog fills a 40-foot cube centered on a point the colgera can see within 120 feet of it. The fog spreads around corners, and the area becomes heavily obscured. Each creature in the fog when it appears, or that ends its turn within it, must make a DC 14 Constitution saving throw: on a failed save, it is chilled for 1 minute. A creature with resistance to cold damage has advantage on the saving throw, and a creature that is immune to cold damage is unaffected. A chilled creature has its speed halved, takes a -2 penalty to its AC and Dexterity saving throws, can use either a bonus action or an action on its turn, and can only make one attack per turn. A chilled creature can repeat the saving throw at the end of its turn: on a success, the effect ends for it. The effect also ends for a chilled creature if it takes fire damage. The fog is dispersed by winds of at least 20 miles per hour, but otherwise lasts until the colgera uses this lair action again or dies.

Regional Effects

The land within 5 miles of the colgera's lair is covered in a perpetual snowstorm. The DC to resist the effects of extreme cold increases to 12; creatures with resistance to cold damage are no longer unaffected by this cold, but they have advantage on the saving throw. The pall of snow makes the area lightly obscured at all times.