Celestial Guardian of Lightning

Spellcasting. The Celestial Guardian of Lightning is a spellcaster. Its spellcasting ability is Wisdom (spell save DC 17, +7 to hit with spell attacks). The Celestial Guardian of Lightning has following spells prepared: 

• Cantrips (at will): Booming Blade, Eldritch Blast, Lightning Lure
• 1st level (9 slots): Catapult, Chaos Bolt, Magic Missile, Shield, Thunderwave, Witch Bolt
• 2nd level (8 slots): Misty Step, Shatter
• 3rd level (7 slots): Blink, Call Lightning, Counterspell, Haste, Lightning Bolt, Slow, Thunder Step, Wind Wall
• 4th level (6 slots): Charm Monster, Dimension Door, Greater Invisibility, Storm Sphere
• 5th level (5 slots): Control Winds, Dominate Person, Far Step, Maelstrom
• 6th level (4 slots): Chain Lightning, Disintegrate
• 7th level (3 slots): Fire Storm, Prismatic Spray
• 8th level (2 slots): Control Weather
• 9th level (2 slots): Prismatic Wall, Storm of Vengeance

Multiattack: The Guardian makes 2 melee attacks with the thunder staff.

Thunder Staff: Melee Weapon Attack: +12 to hit, reach 10ft., 1 target. Hit: 19 (2d10+9) bludgeoning damage and 31 (3d12+13) lightning damage.

Storm Strike: Ranged Weapon Attack: +13 to hit, range 50/80ft., 1 target. Hit: 28 (4d8+12) thunder damage and 28 (4d8+12) lightning damage.

Storm Beam (Recharge 6): 100ft long 5ft wide beam of crackling Lightning energy. All creatures in the beam must make a Dexterity Save (DC17), on a failed save take 65 (8d12+17) lightning damage.