Hellstar (5e Creature)
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Gargantuan elemental, neutral evil
Saving Throws Wis +7
Death Throes. When the hellstar is reduced to 0 hit points, it immediately perishes in a massive explosion. All creatures within 1,000 feet of the hellstar must make a DC 21 Dexterity saving throw, taking 27 (5d10) fire damage and 27 (5d10) lightning damage on a failed save, or half as much on a successful one.
Plasma Form. The hellstar can move through a space as narrow as 5 feet wide without squeezing. A creature that touches the hellstar or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage and 5 (1d10) lightning damage. In addition, the elemental can enter a hostile creature's space and stop there. The first time it enters a creature's space on a turn, that creature takes 5 (1d10) fire damage and 5 (1d10) lightning damage and catches fire, until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.
Plasma Absorption. Whenever the hellstar is subjected to fire or lightning damage, it takes no damage and instead regains a number of hit points equal to the fire or lightning damage dealt.
Radiation. The hellstar sheds bright light in a 120-foot radius and dim light for an additional 120 feet. Creatures and objects that start their turn in the hellstar's bright light take 5 (1d10) fire damage and 5 (1d10) necrotic damage.
Spellcasting. The hellstar is a 20th-level spellcaster. It's spellcasting ability is its Charisma (spell save DC 20, +12 to hit with spell attacks). The hellfire knows the following sorcerer spells:
Cantrips (at will): dancing lights, fire bolt, light, message, minor illusion, true strike
Solar Arc. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 33 (5d10 + 6) fire damage and 33 (5d10 + 6) lightning damage. If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.
The temperature continues to rise as a burning red sun rises over the horizon. It is almost as if the sun itself were coming closer to the planet... to your horror, the sun begins to grow, and expand, as it rushes towards you... you can almost make out a cruel demonic face within its painful light...
Evil fire elementals who have absorbed the power of hellfire into their being usually perish, but a few managed to harness the energy, bloating to tremendous size as their bodies become a hellfire engine generating their own unstoppable flame. They sail above the skies, appearing to be bright stars or the sun itself, then dive bomb the surface and burn everything to ash, leaving terror and destruction in its wake.