Aether Mephit (5e Creature)
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Small elemental, neutral evil
Damage Resistances acid, necrotic, psychic, radiant; piercing and slashing from magical attacks
Death Burst. When the mephit dies, it explodes in a burst of pure magic in a 5-foot radius, ending all magical effects within the area as if casting dispel magic as a 9th-level spell in the area. Each creature within the area must make a DC 20 Dexterity saving throw. On a failed save, the creature takes 45 (12d6) force damage and cannot cast spells for 1 hour or until it finishes a short rest or long rest. On a successful save, the creature takes half as much damage and does not suffer other effects.
Limited Magic Immunity. The mephit cannot be affected or detected by spells of 6th level or lower unless it wishes to be. It has advantage on saving throws against all other spells and magical effects.
Innate Spellcasting. The mephit's innate spellcasting ability is Charisma (spell save DC 21). It can innately cast the following spells at the lowest level, requiring no material components.
Claws. Melee Weapon Attack: +13 to hit, reach 5 ft., one creature. Hit: 9 (1d4+7) slashing damage plus 25 (10d4) force damage.
Aether Breath (Recharge 6). The mephit exhales a 15-foot cone of pure magic. Each creature in that area must make a DC 21 Dexterity saving throw, taking 21 (6d6) force damage on a failed save, and half as much damage on a successful one. Additionally, if a creature with at least one spell slot fails the saving throw, it must expend one spell slot it has.
Invisibility. The mephit magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell).
The mephit can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The mephit regains spent legendary actions at the start of its turn.
Flight. The mephit flies up to half its flying speed.
Claws. The mephit makes a claw attack.
Aether Breath (Costs 2 Actions). The mephit uses its Aether Breath action.
Spell (Costs 2 Actions). The mephit casts a spell from its Innate Spellcasting feature.
The presence of an aether mephit is not found naturally. This is because of its physiological structure, which involves all four major elements of the Elemental Planes fused into a stable state, commonly known as "aether." Such occasion is very rare, if not downright nonexistent, and even if aether is created, its quantity would be too little to form an elemental delinquent known as mephits.
Either by a manic experiment, a catastrophe involving masssive elemental energy, or by a sheer luck that happens once every green-cheese moon, an aether mephit manifests itself into the Elemental Chaos, and in no time, in the Material Planes. However strong, however smart, and however malicious, a mephit is, after all, a mephit, prone to cause mischiefs for the fun of it. Of course, the aether mephit being one of the most powerful entity in the Elemental Planes, its "mischief" often devastates an entire country, if not a continent.