Adult Chromium Dragon

Ice Walk. The dragon can move across and climb icy surfaces without needing to make an ability check. Additionally, Difficult Terrain composed of ice or snow doesn’t cost it extra movement.

Metalsense. The dragon can supernaturally sense non-precious metals (such as iron, steel, or bronze) within 120 feet of itself if the metal is not behind Total Cover. The dragon cannot be Surprised by any creature using armor or weapons made from non-precious metals.

Legendary Resistance (3/Day, or 4/Day in Lair). If the dragon fails a saving throw, they can choose to succeed instead.

Multiattack. The dragon makes three Rend attacks. It can replace an attack with a use of (A) Slowing Breath or (B) Spellcasting to cast Rime’s Binding Ice.

Rend. Melee Attack Roll: +14, reach 10 ft. Hit: 17 (2d8 + 8) Slashing damage plus 5 (1d10) Cold damage.

Cold Breath (Recharge 5–6). Dexterity Saving Throw: DC 17, each creature in a 60-foot Cone. Failure: 76 (17d8) Cold damage. Success: Half damage.

Slowing Breath. Constitution Saving Throw: DC 17, each creature in a 60-foot-long, 5-foot-wide Line. Failure: The target can’t take Reactions; its Speed is halved; and it can take either an action or a Bonus Action on its turn, not both. This effect lasts until the end of its next turn. 

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 16):

At Will: Fear, Rime’s Binding Ice, Shape Water

1/Day Each: Eyebite

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Frightful Presence. The dragon uses Spellcasting to cast Fear. The dragon can’t take this action again until the start of its next turn.

Ice Trap. The dragon uses Spellcasting to cast Rime's Binding Ice.

Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.