Salamanders are the fiery analogue to water weirds, galeb duhrs and invisible stalkers, but they’re significantly more independent-minded, serving only efreets (and those only reluctantly and resentfully). They have a society of their own, on the Elemental Plane of Fire, and if they’re hanging out on the material plane, they’re probably doing so against their will.
As fighters, salamanders are shock troops. Their exceptional Strength is coupled with high Dexterity and Constitution (their Con is higher than their Dex, though not significantly so): they can engage in either toe-to-toe slugfests or hit-and-run attacks, but in general they’ll favor melee over ranged attacks, because they can do much more damage at close range.
Salamanders are immune to fire attacks, vulnerable to cold attacks and resistant to physical damage from nonmagical weapons. Thus, they’re more cautious around foes who wield magic weapons, as well as spellcasters who sling frost spells. Because of their choleric temperament, however, this caution is as likely to result in focused fire (pun intended) as in avoidance.
The salamander wields a spear, most likely two-handed, since (a) their armor class includes no shield or other off-hand weapon and (b) it does more damage that way. Lacking any clothing or tack, it has no way of transporting any weapon other than the one it holds in its hands—yet another reason why it would rather jab with its spear than hurl it. If it throws that spear at an enemy, it’s got no more spear.
Thus, a salamander closes quickly with its foes and immediately Multiattacks with both its tail and its spear. The tail attack comes first, since a successful tail hit grapples and restrains its target, thus granting advantage on the follow-up spear attack. It also grants automatic tail hits on subsequent turns, as long as the target remains grappled—and since a grappled creature is, by definition, touching the salamander, Heated Body does additional fire damage, presumably on that creature’s turn.
The Monster Manual is vague on how this works, but the way I read it, it’s simply a side effect of being so close to the salamander and therefore takes place at the first moment it can. Thus, if you start your turn grappled, you get burned at the start of your turn. If you aren’t grappled, but you come close enough to the salamander to touch it or hit it with a melee attack, you get burned when you do so. But if you’re grappled by a salamander and you attack it while grappled, you don’t take Heated Body damage twice (“A creature that touches the salamander or hits it with a melee attack while within 5 feet of it”—emphasis mine). It’s a once-per-turn thing.
This is pretty much it. A salamander doesn’t have high enough Wisdom to target its foes carefully, but it does have high enough Intelligence to switch gears if it realizes someone’s using a magic weapon or slinging ice spells. If it’s near enough to close with a spellslinger or an attacker with a magic ranged weapon, it will charge that enemy and try to grab him or her with its tail. An opponent with a magic melee weapon presents a trickier problem. Heated Body still does damage to that opponent if he or she lands a hit, but ideally, the salamander would rather not be hit by that weapon at all. How to destroy the wielder while avoiding the weapon?
Thanks to the salamander’s Large size and exceptional Strength, a little-used optional rule on page 271 of the Dungeon Master’s Guide offers a solution: it can use its action to Disarm its opponent, an ability check that it has advantage on if its opponent is wielding his or her weapon one-handed and no disadvantage on if the opponent wields it two-handed. Then, as a free interaction with an object (Player’s Handbook, page 190), it can smack that weapon out of reach with its tail. If the opponent tries to go after it and pick it back up, the salamander will then be able to make an opportunity attack!
Additionally, salamanders speak their own primordial language, Ignan, the common tongue of the Elemental Plane of Fire. A salamander attacked by an enemy with a magic weapon will call out that fact to its allies. If that enemy is disarmed and his or her weapon smacked away, another salamander may rush in to pick it up (or, if it’s a frost brand weapon, hurl the odious thing far, far away) or attack that same enemy from another direction (see Flanking, DMG 251).
A salamander’s self-preservation instinct kicks in when it’s seriously wounded (reduced to 36 hp or fewer). Not quite smart or self-disciplined enough to Disengage but not so dim as to merely flee, the salamander will Dodge as it retreats at its full movement speed.
A fire snake is a juvenile salamander. It also has the Heated Body feature, a dual Multiattack (bite plus tail), and the same damage immunity, vulnerability and resistance as the mature salamander has. But it’s not especially strong, tough or bright. It fights solely by instinct, and although it’s as truculent as its big brothers and sisters are, it can’t withstand a sustained engagement and has to rely on hit-and-run attacks.
Fire snakes in the company of adult salamanders will fight differently from a nest of fire snakes with no big ’uns around. While the adult salamanders do their thing, fire snakes will nip at the heels of the salamanders’ opponents (again, see Flanking). As soon as an opponent turns around and starts attacking a fire snake, it will Dash away, without regard for opportunity attacks. If it’s not seriously wounded (reduced to 8 hp or fewer), it will then come back and resume attacking as soon as its opponent’s attention is occupied by an adult salamander again. But a group of fire snakes without an adult around will attack willy-nilly, using half their movement to close distance with an opponent, Multiattacking (action), then using the other half of their movement to back away again—again, without regard for opportunity attacks. Any foe who makes an opportunity attack against a fire snake is just asking to get burned, anyway.
Next: elite giants from Volo’s Guide to Monsters.