Zappergeist (5e Creature)
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Medium undead, unaligned
Damage Resistances acid, cold, fire, thunder
Charged Body. A creature that touches the zappergeist or hits it with a melee attack while within 5 feet of it takes 6 (1d12) lightning damage.
Ethereal Sight. The zappergeist can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.
Incorporeal Movement. The zappergeist can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.
Lightning Absorption. Whenever the zappergeist is subjected to lightning damage, it takes no damage and regains a number of hit points equal to the lightning damage dealt.
Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 8 (2d6 + 1) piercing damage plus 32 (3d20 + 1) lightning damage.
Etherealness. The zappergeist enters the Ethereal Plane from the Material Plane, or vice versa. It is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.
The ghost of a long-dead predator. The zappergeist is nearly capable of sustaining its metabolism on electricity alone, reluctantly supplementing this "diet" with organic material as needed. It can store thousands of volts in specialized cells filling its hollow but tough bones, and can discharge excess energy to protect itself. Its innermost jaws are particularly conductive, and can release the monster's entire remaining charge in one deadly, short-range bolt under dire enough circumstances. When it passes through matter on the material plane, it leaves behind ectoplasmic slime which smells extremely acidic, stings to the touch, and emits a pale blue glow, but is oddly enough not conductive to electricity. If necessary, it may saturate allies in its slime to avoid harming them.