Xurkitree (5e Creature)
From D&D Wiki
Large aberration, neutral
Beast Boost. When Xurkitree reduces a hostile creature to 0 hit points, it deals an additional 8d6 lighting damage with all its attacks. This bonus is cumulative, but resets when Xurkitree takes a long rest.
Thunderbolt. Ranged Spell Attack: +9 to hit, range 300 ft., one target. Hit: 52 (15d6) lightning damage.
Discharge. All creatures within 30 ft. of Xurkitree must make a DC 17 Constitution saving throw, taking 35 (10d6) lightning damage on a failed save, or half as much damage on a successful one.
Xurkitree's powerful electric blasts are unparalleled in strength, and only grow more powerful when it defeats its enemies. Although its attacks are powerful, it has very weak defenses and lacks variety in its attacks.