Legendary Resistance (3/Day).

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

Actions

Multiattack.

The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite.

Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage.

Claw.

Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail.

Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning 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.

Breath Weapons (Recharge 5–6).

The dragon uses one of the following breath weapons.

Acid Breath. The dragon exhales acid in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 54 (12d8) acid damage on a failed save, or half as much damage on a successful one.
Slowing Breath. The dragon exhales gas in a 60-foot cone. Each creature in that area must succeed on a DC 18 Constitution saving throw. On a failed save, the creature can't use reactions, its speed is halved, and it can't make more than one attack on its turn. In addition, the creature can use either an action or a bonus action on its turn, but not both. These effects last for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself with a successful save.

Legendary Actions

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action 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 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Lair Actions

On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects:

The dragon chooses a point on the ground that it can see within 120 feet of it. Stone spikes sprout from the ground in a 20-foot radius centered on that point. The effect is otherwise identical to the spike growth spell and lasts until the dragon uses this lair action again or until the dragon dies.
The dragon chooses a 10-foot-square area on the ground that it can see within 120 feet of it. The ground in that area turns into 3-foot-deep mud. Each creature on the ground in that area when the mud appears must succeed on a DC 15 Dexterity saving throw or sink into the mud and become restrained. A creature can take an action to attempt a DC 15 Strength check, freeing itself or another creature within its reach and ending the restrained condition on a success. Moving 1 foot in the mud costs 2 feet of movement. On initiative count 20 on the next round, the mud hardens, and the Strength DC to work free increases to 20.

Additional Lair Actions[–]

At your discretion, a legendary (adult or ancient) copper dragon can use one or both of the following additional lair actions while in its lair:

Laughing Gas. The dragon chooses a point on the ground that it can see within 120 feet of it. A cloud of pink gas fills a 20-foot-radius sphere centered on that point. Each creature in that area that fails a DC 15 Wisdom saving throw is incapacitated with laughter until the end of its next turn.
Torpid Energy. The dragon chooses a creature it can see within 120 feet of it. If the target fails a DC 15 Constitution saving throw, its speed is halved, and it can't use reactions or bonus actions until the end of its next turn.

Regional Effects

The region containing a legendary copper dragon's lair is warped by the dragon's magic, which creates one or more of the following effects:

Magic carvings of the dragon's smiling visage can be seen worked into stone terrain and objects within 6 miles of the dragon's lair.
Tiny beasts such as rodents and birds that are normally unable to speak gain the magical ability to speak and understand Draconic while within 1 mile of the dragon's lair. These creatures speak well of the dragon, but can't divulge its whereabouts.
Intelligent creatures within 1 mile of the dragon's lair are prone to fits of giggling. Even serious matters suddenly seem amusing.

If the dragon dies, the magic carvings fade over the course of 1d10 days. The other effects end immediately.

Additional Regional Effects[–]

Either of these effects might appear in the area around a copper dragon's lair, in addition to or instead of the effects described in the Monster Manual:

Distant Melodies. The ethereal music of woodwinds and bells can be heard carried on the wind within 1 mile of the dragon's lair.
Starlit Stones. Standing stones are common on hilltops within 1 mile of the dragon's lair. The stones shed dim light in a 10-foot radius at night. (If the dragon dies, the stones remain, but they no longer shed light.)

Adult Copper Dragon