Ancient Silver Dragon

If the monster fails a saving throw, it can choose to succeed instead.

The monster makes three Rend attacks. It can replace one attack with a use of (A) Paralyzing Breath or (B) Spellcasting to cast Ice Knife (level 2 version).

Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 2d8+10 slashing damage plus 2d8 cold damage.

The monster exhales a 90-foot cone of cold. Each creature in that area must make a DC 24 Constitution saving throw, taking 15d8 cold damage on a failed save, or half as much damage on a successful one.

The monster exhales a 90-foot cone of paralytic gas. Each creature in that area must make a DC 24 Constitution saving throw. On a failed save, a creature is incapacitated until the end of its next turn, when it repeats the save. On a second failed save, the creature is paralyzed for 1 minute, repeating the save at the end of each of its turns, ending the effect on itself on a success. After 1 minute, it succeeds automatically.

The monster casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 24, +16 to hit with spell attacks): At will: Detect Magic, Hold Monster, Ice Knife (level 2 version), Shapechange (Beast or Humanoid form only, no Temporary Hit Points gained from the spell, and no Concentration or Temporary Hit Points required to maintain the spell). 1/Day each: Control Weather, Ice Storm (level 7 version), Teleport, Zone of Truth.