Adult Copper 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) Slowing Breath or (B) Spellcasting to cast Mind Spike (level 4 version).

Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) slashing damage plus 4 (1d8) acid damage.

Dexterity Saving Throw: DC 18, each creature in a 20-foot-long, 5-foot-wide Line. Failure: 54 (12d8) acid damage. Success: Half damage.

Constitution Saving Throw: DC 18, each creature in a 60-foot Cone. 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.

The monster casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 17): At Will: Detect Magic, Mind Spike (level 4 version), Minor Illusion, 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: Greater Restoration, Major Image.