Arcane Wyvern

Reflective Scales. When targeted by a spell, the Arcane Wyvern can use its reaction to cast Counterspell without expending a spell slot. If the spell is successfully countered, the spell is redirected back at the caster.

Multiattack. The wyvern makes two attacks: one with its bite and one with its stinger. While flying, it can use its claws in place of one other attack.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one creature. Hit: 21 (2d12 + 8) piercing damage plus 17 (4d6+3) force damage.

Claws. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 23 (2d12 + 10) slashing damage.

Stinger. Melee Weapon Attack: +10 to hit, reach 15 ft., one creature. Hit: 21 (2d12 + 8) piercing damage. The target must make a DC 18 Constitution saving throw, taking 24 (7d8 + 3) poison damage on a failed save, or half as much damage on a successful one.

Fire Breath (Recharge 4–6). The Arcane Wyvern exhales fire in a 30-foot cone. Each creature in that area must make a DC 15 Dexterity saving throw, taking 42 (12d6) fire damage on a failed save, or half as much damage on a successful one.

Spellcasting. The Arcane Wyvern is an 15th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 15, +10 to hit with spell attacks). The Arcane Wyvern has the following spells prepared:

Cantrips (at will): blade ward, eldritch blast, mage hand, produce flame, ray of frost, shocking grasp

1st level (4 slots): command, chaos bolt detect magic, feather fall, magic missile

2nd level (3 slots): dragon's breath,  gust of wind

3rd level (3 slots): cone of cold, fireball, haste, pulse wave

4th level (3 slots): dimension door, greater invisibility

5th level (2 slots): lightning bolt, immolation, wall of force

6th level (1 slot): globe of invulnerability,  dragon's breath

7th level (1 slot): plane shift, true seeing

8th level (1 slot): dominate monster