Slaadi are beings of pure chaos, native to the outer plane of Limbo, vaguely resembling humanoid salamanders. There’s no good reason for them to be hanging out on the prime material plane, but being beings of pure chaos, they don’t need a good reason to be doing anything.
Slaadi come in a variety of colors, tied to their bizarre reproductive cycle. Red slaadi deposit eggs that hatch into slaad tadpoles (I think the writers missed a great opportunity by not calling them “slaadpoles”), which grow up into blue or green slaadi. Blue slaadi, in turn, infect victims with a bacteriophage that transforms them into red or green slaadi. Green slaadi are more powerful and intelligent than red and blue slaadi, and they eventually metamorphose into gray slaadi, which in turn can metamorphose into death slaadi by eating the corpses of other death slaadi.
Being aberrations, slaadi should behave—and fight—in ways that reflect their origin on the plane of chaos, a factor that has to be considered alongside their abilities and features. Slaadi are high-challenge monsters, so as tempting as it may be to ramp up the chaos they create by having the player characters encounter many of them at once, it can be deadly to throw more than one slaad at a party of low- or even intermediate-level PCs. Moreover, their ability to reproduce by turning humanoids into slaadi and slaad hosts can have exponential effects, so even one slaad is a threat that needs to be squelched pronto.
The slaad tadpole is tiny and weak but frisky: it has high Dexterity and proficiency in Stealth. It has few hit points, but it’s resistant to acid, cold, fire, lightning and thunder damage and has advantage on saving throws vs. magical effects. Thus, in a reversal of the more common monster paradigm, regular melee fighters should have no trouble harming it, but spellcasters will be frustrated.
A slaad tadpole’s primary motivation is to grow up into a big slaad. Consequently, it has no desire to hang around and fight anybody. As soon as it emerges from its host, it will flee to a place of hiding, using the Dash action (it’s not bright enough to do anything else). It has no special movement such as swimming, climbing or burrowing, so it will dart under furniture, through cracks in the wall and so forth. It may be helpful to imagine it doing exactly what a rat would do if you spotted one and started chasing it. It will bite only if grabbed. If the PCs try to pursue it, use the Chase rules on pages 252–54 of the Dungeon Master’s Guide—and absolutely use the optional chase complications. I’d even go so far as to say that the slaadpole’s chaotic nature causes complications to occur: if a chase participant rolls 11–20 on the first roll, have him or her roll a second time and use that result. (Having the chase participants roll d10’s—or even d12’s—rather than d20’s is probably going too far.)
Before the PCs discover the slaadpole, and again as soon as it leaves their field of vision, apply its Stealth to its pursuers’ attempts to spot it again (skill contest, Stealth vs. Perception).
Red slaadi and blue slaadi are dumb brutes without Stealth but with the same damage resistances as the slaadpole. They’re vicious toe-to-toe melee fighters, with lots of hit points and very high Strength and Constitution, and their goal is to deposit their eggs or bacteriophages in humanoid hosts, so they’ll want to make as many claw attacks as possible against as many targets as possible. They’re indiscriminate in target selection, directing their attacks at the nearest humanoid enemy whom they haven’t already hit with a claw attack. (Once they’ve clawed a target, they have no way of knowing whether they’ve managed to infect him or her; they just assume success and move on to the next target.) On each turn, they use their Multiattack to claw/claw/bite, attacking the same target again only if both claw attacks miss. Once they’ve clawed every humanoid in the immediate area, they Dash away in search of another group of humanoid targets. If the PCs give chase, consider applying the same chaos-inducing second roll for chase complications rule as described above.
Green slaadi are sentient spellcasters whose primary goal is to discover the key to metamorphosis into gray slaadi, so they’re generally going to try to stay on the down-low. As long as they’re in or near any inhabited area, they use their Shapechanger feature to assume inconspicuous humanoid forms, often those of their former hosts. However, their ability to assume a particular physical form isn’t enough to fully conceal their true nature, so even if they look totally normal and respectable—possibly even attractive—their behavior will be glaringly, unmistakably weird. (For one thing, they no longer speak Common or whatever other language their hosts spoke, only Slaad.) Only if their slaad-nature is discovered and called out will they resort to fighting.
When a green slaad fights, its primary goal is not to kill its opponents but to escape. That being said, killing your pursuers is a reliable way of keeping them from pursuing you, and green slaadi, despite having Intelligence superior to other slaadi’s, still aren’t overly endowed with Wisdom. Also, note their innate ability to cast fireball and their Hurl Flame feature. A panicking green slaad will set lots and lots and lots of stuff on fire.
Let’s evaluate each of its abilities with an eye toward how it can help the green slaad make its getaway (noting, first and foremost, the fact that it doesn’t have proficiency in Stealth):
- Fireball drops the bomb on a sphere 40 feet in diameter—large enough, on average, to char four enemies (per DMG 249), not to mention igniting all flammable objects in the area.
- Fear affects up to three enemies, on average (again, per DMG 249), causing them to drop whatever they’re holding and run the other way if they fail their Wisdom saving throws. It requires concentration to sustain.
- Invisibility allows the green slaad to move unseen, though not to attack or cast spells while invisible. It also requires concentration.
- Detect magic has no bearing on the green slaad’s ability to escape. Its application is in social interaction situations, in which the green slaad—always keen to learn anything that might help it metamorphose into a gray slaad—scans the PCs to O HAI I SEE YOU HAVE A MAGIC ITEM WITH MAGICAL PROPERTIES MAY I LOOK AT IT PRETTY PLEASE? Of course, social interaction with a green slaad is always going to be oddball at best, since unless a party member speaks Slaad, it will have to be conducted via either telepathy or gesticulation.
- Detect thoughts is a useful early-warning system that the green slaad uses constantly to ascertain whether it’s been found out.
- Mage hand, normally, is useful for picking up the teakettle without burning yourself. However, cast by a slaad, it becomes a micro-poltergeist that can slam doors, use objects that are on fire to set other objects on fire, prod animals into stampeding in front of pursuers, yank guards’ weapons out of their scabbards and keyrings off their belts, throw cabbages (not to cause any damage, but simply because throwing cabbages is hilarious) and engage in all sorts of other mischief that doesn’t involve lifting or pushing more than 10 pounds of weight.
- The green slaad’s Multiattack can consist of two uses of Hurl Flame, two staff attacks (in humanoid form), two staff attacks plus a bite (in slaad form) or two claw attacks plus a bite (in slaad form). The melee attacks have a better chance of hitting than the Hurl Flame attack, although as DM you can rule that a Hurl Flame attack that misses its target hits something else and sets it on fire. To account for the difference in attack modifiers, we’ll apply a 77 percent multiplier to Hurl Flame’s damage for the sake of comparison (based on to-hit probabilities vs. target AC 15). Thus, two Hurl Flames = 16 hp damage, two staff attacks = 22 hp damage, staff/staff/bite = 33 hp damage, and claw/claw/bite = 26 hp damage. This tells us that, when mayhem ensues, the green slaad would prefer to revert to its slaad form rather than stay in its humanoid disguise.
Fifth-edition Dungeons and Dragons bases its combat-balancing decisions on the assumption that combat encounters last three rounds, but to take down a green slaad that quickly, PCs will have to be capable of dealing a combined 49 hp of damage per round (thanks to its Regeneration feature), more than that if they’re relying on magic to deal the damage. Even so, spending one turn to revert to slaad form will cost the green slaad precious time, during which the PCs can deal it quite a bit of harm.
So it won’t do it the simple way. And anyway, why would a slaad do anything the simple way?
The first thing a busted slaad does is turn invisible. The next thing it does is revert to slaad form, which it can do without becoming visible, because changing shape is neither an attack nor a spell. Then it attacks. Or maybe it doesn’t even attack. Maybe it just runs away, still invisible. It can keep that spell going for a full hour, after all.
But maybe the PCs have means of detecting or tracking an invisible opponent. If the green slaad observes that it’s being pursued despite being invisible, then it drops fireball and fear on its pursuers, the former while still invisible (thereby rendering it visible to all). It doesn’t stop fleeing, although while it’s using these actions to disrupt pursuit, it can’t also Dash. If the environment contains enough loose and/or flammable objects that it can use to cause further mayhem, it may spend actions on mage hand or Hurl Flame, but most likely, once it’s used fireball and fear, it will simply Dash until it escapes or is cornered. If cornered, it will fight with its staff and bite, using invisibility a second time if an escape path presents itself. Given a choice between fleeing and fighting, it will always prefer to flee.
Gray slaadi, on the other hand, have reached the pinnacle of their “natural” metamorphosis and relish fighting. In fact, they’re usually on the prime material plane in the first place on some specific mission of mayhem. They can cast invisibility at will, but rather than use it to escape, they’ll use it to approach enemies and get the jump on them. Although they natively speak only Slaad, they can use tongues to disguise their inability to speak the PCs’ language(s). Their emergency exit, if somehow the PCs manage to seriously injure them (reduce them to 50 hp or fewer), is plane shift. But even gray slaadi have low Wisdom, and their choice of targets will be more or less random, unless they’re on a mission to attack one or more specific people.
Gray slaadi probably won’t bother to use fear against enemies they mean to fight, only against bystanders who get in the way of whatever mission they may be on. They can cast major image at will, and this can be useful for creating distractions during chases or even entirely fake personae for them to interact with the PCs through. A gray slaad may disguise itself as a VIP and conjure up a major image of a bodyguard or adviser—or vice versa! For super-duper mayhem during combat, gray slaadi can cast fly, gaining a flying speed of 60 feet and allowing them to swoop in to attack twice with their greatswords and once with their bite, then soar back into the air, out of reach of melee attacks. (With AC 18, they’re indifferent to opportunity attacks.) And, of course, they still have good ol’ fireball, only unlike green slaadi, they can cast it twice per day.
In general, having higher Strength and Dexterity than Constitution (though all three are very high), they will favor skirmishing and dealing large amounts of damage in single hits over staying in one place and fighting toe-to-toe. As long as they have their greatswords, they’ll favor these over their claws.
According to the Monster Manual flavor text, death slaadi lead invasion forces of red and blue slaadi to ravage other planes. Remember how I said that just one slaad was a potentially deadly encounter? A death slaad accompanied by many red and blue slaadi is a potentially deadly encounter even for top-tier adventurers. When you design death slaad encounters, make absolutely certain you’re not burdening your players with an enemy they’re not equipped to take on.
Death slaadi don’t bother with skirmishing—they’re brutes. When they cast fly, they do it to close quickly with an enemy they want to pound the stuffing out of. They also have a bizarrely high Charisma for being hideous, spiky salamander people from a chaos plane. I can only assume this is to help them blend in better while Shapechanged into humanoid form. They’ll still be weird, but . . . I don’t know . . . intriguingly weird, maybe? Compellingly weird?
In addition to all the powers of the gray slaad, death slaadi have one daily use of cloudkill. There’s a difference between how they use fireball and how they use cloudkill: Fireball is for causing mayhem and, incidentally, doing damage to pesky PCs getting in the death slaad’s way. Cloudkill is specifically for killing people the death slaad wants to kill.
Like gray slaadi, death slaadi will prefer to use their greatswords rather than their claws in melee combat, and they’ll prefer to fight in their slaad form rather than their humanoid form, in order to include biting in their Multiattack. They’ll retreat when seriously injured (reduced to 68 hp or fewer), using plane shift to escape.
Alone among slaadi, death slaadi are canny enough to be able to guess at PCs’ alignments, and they’ll zero in on lawful characters. After defeating one, they’ll move on to another lawful character, who may not necessarily be the nearest. If and when all lawful opponents have been defeated, only then will they move on to other PCs, choosing targets largely at random.