Adult Limestone Dragon

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

Spell Breath (Recharge 5-6). If the limestone dragon sees a spell cast with somatic components, hears a spell cast with verbal components, or sees and hears a spell cast with both components, it can make an Intelligence (Arcana) check against the caster's Spell Save DC. If successful, it will copy the spell cast, and can cast the spell once as a bonus action. The spell copied will be of the same level it was initially cast as. The limestone dragon can't copy the same spell multiple times, but the amount of spells it can copy is limitless. When the limestone dragon casts a copied spell, it does not require material components. 48 hours after a spell was copied, the limestone dragon will lose access to the copied spell. The copied spells that a limestone dragon casts are treated as a breath weapon.

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: +14 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) 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 19 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.

Counterspell. If the limestone dragon has one or more spells stored, it can attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of equal level or lower to the stored spell expended, its spell fails and has no effect. If it is casting a spell of higher level, the limestone dragon must make an Intelligence (Arcana) saving throw. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect.

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 feet of the dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.