Silver dragon

Silver dragons are sociable true dragons who dwell in cold environments, whether mountaintops, caverns, or preferably abandoned humanoid structures, but often spend much of their time traveling as humanoids.

Appearance
Aside from the distinctive color of its scales (developing from a blue-grey with silver highlights to a uniform metallic sheen with age), a silver dragon is recognized by its beard-like chin spikes, high-set eyes, and head-to-tail frill.

Abilities
The following is taken from the Monster Manual, 5th Edition; none of the abilities have yet been demonstrated onstream.
 * Damage immunity: cold
 * Cold Breath: Exhales a cone of icy air, requiring a Constitution saving throw to take half damage.
 * Paralyzing Breath: Exhales a cone of paralyzing gas, requiring a Constitution saving throw to avoid being paralyzed for 1 minute, repeating the saving throw at the end of each turn.
 * (Adult and older) Frightful Presence: Each creature of the dragon's choice must succeed at a Wisdom saving throw or become frightened for 1 minute, or until they succeed at the saving throw at the end of their turn.
 * (Adult and older) Change Shape: Polymorph into a humanoid or beast with a Challenge Rating no higher than the dragon's, or back into its true form. Any equipment it is carrying can be absorbed or carried/worn by the new form or absorbed. The new form still has the dragon's lair actions (see below), personality, mental ability scores, hit points, and ability to speak, but otherwise gains the abilities and features of the new form.
 * Lair actions:
 * An icy wind extinguishes flames, disperses gases and vapors, and forces each nearby creature to succeed at a Constitution saving throw or take cold damage.
 * Creates fog as with the fog cloud spell until initiative count 20 of the next round.

History
Although silver dragons are typically good and friendly, the two known silver dragons have both unaccountably turned to destruction, at least temporarily.

Ages ago, Karkethzerethzerus (Karketh for short) annihilated a nation of wood elves and centaurs using the energies of the Shadowfell, turning that region of the Miskath Strand into a petrified woodland now called Strathfell. As of 836 PD, he is an ancient shadow dragon ruling the area as a swaggering yet paranoid tyrant, with evil minions like darklings and meenlocks traveling through rifts between Strathfell and the Shadowfell. The few remaining good-aligned centaurs (the descendants of the ones slayed by Karketh) still battle the Sable Despoiler and his minions.

Far away on Tal'Dorei, at some point between 812 PD and 836 PD, Saldarthoryn started rampaging through Tal'Dorei and sowing chaos, to the point that The Wonderworker, the mysterious leader of the League of Miracles, went out to meet the dragon, stopping her and healing her twisted mind.