Ancient Lighting Guardian

Amphibious. The guardian can breathe air and water.

Spider Climb. The spider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The guardian makes three attacks: one with its tentacles and two with its stomp.

Tentacles. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 9 (2d6 + 5) bludgeoning damage plus 5 (1d6) lightning damage.

Stomp. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage.

Ancient Lighting. The Guardian uses Lighting Breath, and then Lighting Burst

Lightning Breath (Recharge 5–6). The Guardian exhales lightning in an 60-foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 30 (5d12) lightning damage on a failed save, or half as much damage on a successful one.

Lighting Burst. The Guardian expulsé the remaining lightning in an 10-foot radius. Each creature in that area must make a DC 15 Dexterity saving throw, taking 9 (3d6) lightning damage on a failed save, or none on a successful one.