ok this critter might be coming up as a boss in my campaign in the next 6 weeks or so
Here's a rough draft of what I've come up with so far.
They're more-or-less balanced to CR 23 (I hope!). The main points I'm uncertain of is whether the Firepower Cost of the abilities is OK or not.
Still got the
Purifying Pyre and
Create Fire Elemental actions to write up.
Actions
Multiattack. The fire archomental makes three attacks with any combination of firefists and incandescent bolts.
Firefist. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 19 (4d6 + 5) bludgeoning damage plus 35 (10d6) fire 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.
Fireswarm (Costs 4 Firepower). The fire archomental hurls blazing orbs of fire to four different points within 1,000 feet[?]. Each creature in a 40-foot-radius sphere centered on each targeted point must make a Dexterity saving throw. A creature takes 42 (12d6) fire damage and 42 (12d6) bludgeoning damage on a failed save, or half as much damage on a successful one. The spherical effect spreads around corners; a creature in the area of more than one fiery burst is affected only once.
Incandescent Bolt (Costs 1 Firepower). Ranged Weapon Attack: +13 to hit, range 100/400 ft., one target. Hit: 27 (6d8) fire damage plus 27 (6d8) force damage.
Purifying Pyre (Costs 3 Firepower). ???.
???.
Bonus Actions
Cleansing Flame (Costs 1 or 2 Firepower). For 1 firepower, the fire archomental can automatically burns away a single condition spell or magical effect affecting itself.
Alternatively, the archomental can spend 2 firepower and use Cleansing Flame on a creature exposed to its Flame Aura (which includes itself) or that it has hit with an Incandescent Bolt. Any spell of #th level[?] or lower on the target ends. For each magical effect or spell of #th level[?] or higher on the creature, the fire archomental makes a Charisma ability check against the DC of the spell or effect. On a successful check, the spell or effect ends.
Flare (Costs 1 to 4 Firepower). The fire archomental's body becomes blazingly bright. For every point of firepower it spends, it sheds bright light in a 250 foot radius and dim light in an additional 250 foot radius. In addition, every creature within a 30 foot radius per point of firepower spent (i.e. 90 ft. for 3 firepower) must succeed on a DC 20 Constitution saving throw or be blinded until the start of the elemental's next turn.
Incite Ignition (Costs 1 Firepower). The fire archomental selects a target within 100[?] feet. The target must succeed at a DC 20 [Wisdom? Constitution? Best of Wisdom or Constitution?] saving throw or loses any resistance or immunity to fire damage it possesses for 1 minute. The ignited target can repeat the saving throw at the end of each of its turns. If the saving throw is successful, the effect ends on it.
Smoke Cloud. The fire archomental exhales a 60-foot-radius sphere of smoke and embers centered on a point within 40 feet of itself. The sphere spreads around corners, and its area is heavily obscured. It lasts for 1 minute or until a wind of moderate or greater speed (at least 10 miles per hour) disperses it; the cloud moves 10 feet away from the archomental in a direction it chooses at the start of each of its turns. When the cloud appears, any creature in it must make a DC 20 Constitution saving throw or violently cough and choke for 1 round, gaining disadvantage on ability checks. A creature must also make this saving throw when it enters the cloud's area for the first time on a turn or ends its turn there. All standard elementals (air, earth, fire, water) are immune to this choking, as are creatures that do not need to breathe such as undead.
A fire archomental can only maintain one smoke cloud at a time; it can disperse its smoke cloud as a free action.
Stoke Aura (Costs 1 to 3 Firepower). The fire archomental increases the area its Fire Aura covers. The aura's range increases to 60 feet for 1 point of firepower, 80 feet for 2 points, or 100 feet for 3 points.
Legendary Actions
The fire archomental 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 archomental regains spent legendary actions at the start of its turn.
Cleansing Fire (Costs 1 Action). The fire archomental uses Cleansing Flame. [?]
Purifying Fire (Costs 3 Actions). The fire archomental uses Purifying Pyre. [?]
Igniting Fire (Costs 1 Action). The fire archomental uses Incite Ignition. [?]
Smoking Fire (Costs 2 Actions). The fire archomental uses Smoke Cloud. [?]
Create Fire Elemental (Costs # Actions). X. [?]