Adult nickel dragon

Ferrous sense. The nickel dragon can sense and knows the exact location of any ferrous metals within 90ft of themselves.

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Amphibious. The nickel dragon can breathe air and water. 

Innate Spellcasting. The adult nickel dragon's innate spellcasting ability is Wisdom (DC 15). The adult nickel dragon can innately cast the following spells, requiring no material components:

At will: contagion, protection from energy

Multi attack. The adult nickel dragon uses it's frightful prescience then makes a bite attack and two claw attacks. 

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., 1 target. Hit: 16 (2d10 + 6) piercing damage plus 4 (1d8) acid damage.  

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., 1 target. Hit: 12 (2d6 + 6) slashing damage. 

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., 1 target. Hit: 14 (2d8 + 6) slashing damage. 

Frightful Presence. Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dragon’s Frightful Presence for the next 24 hours.

Corrosive breath (Recharges 5/6). The nickel dragon exhales a cloud of corrosive gas in a 60ft cone. Each creature within the radius must make a DC 19 Constitution saving throw or take 60 (15d8) acid damage. Half as much on a successful save.

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time, and only at the end of another creature’s turn. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 ft. of the dragon must succeed on a DC 19 Dexterity saving throw or take 12 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.