Adult Black Dragon

The monster can breathe air and water.

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

The monster makes three attacks. It can replace one attack with a use of to cast Melf's Acid Arrow (level 3 version).

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Dexterity Saving Throw: DC , each in a -foot-long, -foot-wide Line.
Failure: damage.
Success: Half damage.

The monster casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC , +9 to hit with spell attacks):
At Will: Detect Magic, Fear, Melf's Acid Arrow (level 3 version)
1/Day Each: Speak with Dead, Vitriolic Sphere