Arter, The Primal Elemental

Multi-Elemental Being. Arter embodies the five primary elements—fire, water, air, earth, and soul. Its attacks and abilities may deal any of these elemental damage types.

Elemental Form. Arter can move through a space as narrow as 1 inch without squeezing. It can also enter a hostile creature's space and stop there.

Innate Spellcasting. Arter can innately cast the following spells, requiring no material components:

• At will: Control Flames, Ray of Frost, Gust, Acid Splash, Thunderclap
• 3/day each: Burning Hands, Ice Storm, Lightning Bolt, Acid Arrow, Thunderwave

Multiattack. Arter makes three attacks: one with its Slam, one with its Elemental Lash, and one with its Elemental Burst.

Slam. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 2d10 + 6 bludgeoning damage.

Elemental Lash. Ranged Spell Attack: +8 to hit, range 60 ft., one target. Hit: 4d8 damage of a randomly determined elemental type (fire, water, air, earth, or soul).

Elemental Burst. Arter releases a burst of elemental energy in a 20-foot radius centered on itself. Each creature in that area must make a DC 18 Dexterity saving throw, taking 6d6 fire, water, air, earth, and soul damage on a failed save, or half as much on a successful one.

Elemental Shift. Arter can shift its elemental composition, altering its resistances and vulnerabilities. As a bonus action, it can choose to gain resistance to one elemental damage type and vulnerability to another. This effect lasts until the start of its next turn.

Elemental Defense. When Arter is targeted by a spell or ability that deals fire, water, air, earth, or soul damage, it can use its reaction to gain resistance to that type of damage until the start of its next turn.

Elemental Wave (Costs 2 Actions). Arter releases a wave of elemental energy in a 30-foot cone. Creatures in the area must make a DC 18 Dexterity saving throw, taking 4d8 damage of a randomly determined elemental type (fire, water, air, earth, or soul) on a failed save, or half as much on a successful one.

Elemental Resilience (Costs 3 Actions). Arter gains temporary hit points equal to 2d10 plus its Constitution modifier. These temporary hit points last for 1 minute.

Primal Fusion (Mythical Action). Arter merges with the primal forces around it, gaining enhanced abilities. For 1 minute, Arter's attacks deal maximum damage, and it gains advantage on saving throws. Additionally, it can use Elemental Burst as a bonus action. Once Arter uses Primal Fusion, it can't use it again until it finishes a long rest.