Elemental myrmidons are categorized as elementals, but they also have something of the construct about them, since their essences are summoned into suits of plate armor and armed with weapons of indisputable solidity, and since they follow their summoners’ commands without free will.
More intelligent than ordinary elementals—and far more intelligent than elder elementals—elemental myrmidons have sufficient cognitive candlepower to understand and respond to what’s going on in a battle, if not to assess opponents’ weaknesses or devise clever plans. Each has one outstanding physical attribute: Dexterity in the case of the fire elemental myrmidon, Strength in the other three. Their Wisdom and Charisma are average.
Elemental myrmidons all wear plate armor and have resistance to physical damage from nonmagical attacks. They’re immune to poison damage and can’t be paralyzed, petrified, poisoned or proned. Their weapon attacks are magical, they have darkvision (as with the elder elementals, I construe this as indicating more an indifference to lighting conditions than an actual preference for dim light or darkness), and each of them has a single potent, slow-to-recharge special melee attack in addition to a melee Multiattack.
None of the four types of elemental myrmidon has a ranged attack. Even if they’re not brutes per se—and except for the earth elemental myrmidon, none of them is—they’re equipped only for melee combat, so the only tactical decisions for them to make are whom to target and when to use their special attacks.
The air elemental myrmidon’s special attack is Lightning Strike, which does bonus lightning damage to a single target of its flail and may stun the target. In a normal Multiattack, the AEM gets to make three flail attacks, for 25.5 total average damage. In contrast, a flail hit with Lightning Strike does an average of 8.5 bludgeoning plus 18 lightning damage, a total of 26.5. That’s not a significant difference at all—and if the AEM misses, it still has to wait till it rolls a 6 to use this ability again—so the real benefit of Lightning Strike lies in the potential to stun.
The Constitution save DC of 13 isn’t very high. Most mid- to high-level adventurers will have little trouble beating it; a mid- to high-level fighter, barbarian or even sorcerer (thanks to save proficiency) will have no trouble at all. The AEM therefore reserves this feature for opponents who are clearly relying on their Dexterity, rather than their Constitution, as their primary defensive ability: shock attackers like rogues and monks, backline marksmen, and glass-cannon spellcasters. Of these, the marksmen are the lowest-priority targets, unless they’re using magic weapons or ammunition. If the AEM is ever blinded, restrained, stunned or subjected to any other debilitating condition it’s not immune to, it also employs Lightning Strike against whichever opponent was responsible for it as soon as the condition wears off.
Between their high armor class and their resistance to nonmagical weapons, AEMs don’t have to worry themselves much about opportunity strikes; plus, they can hover. So the tactic of waiting 10 feet in the air between rounds, flying in to strike, then flying back out of reach is doable. But if, while doing this, they take two opportunity hits that do full damage, either in the same turn or on two consecutive turns, they ditch this maneuver and stick with straight melee engagement, breaking off only to use Lightning Strike against an opponent of one of the types described above. Whenever it succeeds in stunning a foe with Lightning Strike, it always follows up with a Multiattack against the same target on its next turn, since it gains advantage on its attack rolls.
The earth elemental myrmidon’s special attack is Thunderous Strike, which does bonus thunder damage to a single target of its maul and may knock the target prone. Comparing the damage of this special attack to a normal Multiattack, the basic Multi does an average of 22 bludgeoning damage, while Thunderous Strike does an average 27.5 bludgeoning-plus-thunder, stacking up a bit more favorably—especially with the added possibility of the prone condition.
Thunderous Strike’s save DC is 14: not a whole lot better than Lightning Strike’s DC 13. It’s a Strength save, making it particularly weak against fighters, rangers, barbies and monks but also not that great against paladins and melee-fighting clerics. At the same time, the EEM has no particularly good movement ability and neither reason nor inclination to leave the thick of a battle to wander around the perimeter, picking off archers or spellcasters.
So what’s left? Support-oriented bards, druids—and rogues. Oh, yeah. I mean, it’s just so satisfying to smash one of those pesky little sneaks like a bug, isn’t it? Then again, even an effective Sneak Attack is going to do only half damage if the weapon delivering it isn’t magical. So let’s say that a Thunderous Strike against one of these three classes is provoked by either moderate damage (39 points or more) from a nonmagical weapon attack; light damage (13 points or more) from a magical attack or effect; or being subjected to any debilitating condition it’s not immune to.
The fire elemental myrmidon’s special attack is Fiery Strikes, which just layers additional fire damage on top of its Multiattack. It requires no saving throw and doesn’t reduce the number of attacks the FEM gets to make. There’s no reason for it not to use this ability whenever it’s available, against whomever it would normally attack—although subjecting it to any debilitating condition it’s not immune to will draw its ire as soon as that condition wears off. Because of its Water Susceptibility, it avoids water—but it’s not vulnerable to water or to cold damage, so it has no reason to react to them in any particular way. In fact, it has no feature that suggests any specific targeting criterion. You can run an FEM on autopilot.
The water elemental myrmidon’s special attack is Freezing Strikes (“Behold the power of Hypothermia!”), which layers additional cold damage on top of its Multiattack. But there’s a subtle difference between this and Fiery Strikes: a successful Freezing Strike hit slows the target temporarily. This gives the WEM an incentive to use it against skirmishers and shock attackers who are using their mobility to dart in and out of its reach. Subjecting the WEM to a debilitating condition it’s not immune to also provokes it to target the opponent responsible with a Freezing Strike. Anytime a WEM successfully slows an opponent with Freezing Strikes, it chases him or her down and follows up with a Multiattack against him or her on its next turn.
The WEM has a 40-foot swimming speed, so if the combat encounter is taking place in water, it can pull the same stunt as the AEM, only instead of flying in and out of melee range, it swims in and out of melee range, takes advantage of the fact that its opponents can’t swim as fast. If it notices that one of its opponents isn’t limited in this way, that opponent becomes the target of a Freezing Strike.
As long as targets for it exist, the WEM will use Freezing Strikes whenever that ability is available to it. Also, because it doesn’t carry a shield, it always wields its trident two-handed.
Because, like constructs, elemental myrmidons are bound to their summoners’ will, they can exercise no discretion regarding whether or when to retreat. If they’re ordered to retreat, they retreat. If not, they fight until they’re destroyed.
Next, at the request of multiple readers: the kraken priest.