Arachnotron (5e Creature)
From D&D Wiki
Large fiend (cybrid), chaotic evil
Saving Throws Str +4
Stomp. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d10 + 1) bludgeoning damage.
Plasma Gun Burst. The arachnotron fires a spray of plasma bolts in a 10-foot-cube area within 40 feet. Each creature in that area must succeed on a DC 15 Dexterity saving throw or take 16 (3d10) lightning damage.
Plasma Gun Shot. Ranged Weapon Attack: +7 to hit, range 40/120. Hit: 20 (3d10 + 4) lightning damage.
An arachnotron is a cybrid demon with an upper body composed of brain-like matter mounted on a mechanical chassis with four robotic legs. They have glassy-blue eyes flanked by withered, vestigial arms. The chassis has an integrated plasma gun. They move and react quickly.