An old-school monster dating all the way back to the 1974 Greyhawk supplement, the displacer beast is a panther-like creature that walks on six legs but attacks with a pair of long, sinuous tentacles emerging from its shoulders. Its name comes from its power to make itself appear to be several feet from where it actually is.
Aside from this passive feature, there’s not much in the displacer beast’s stat block to make it anything but a straightforward brute. Its primary physical abilities are Strength and Constitution, its 40-foot movement speed makes charging a snap, and it has no feature that allows or encourages a unique method of attack.
So to find a displacer beast fighting style that differs at all from that of other “Rrrrahhhh, bash bash bash” brutes, we have to look to three things: its armor class, its reach and the Monster Manual flavor text.
For a brute, the displacer beast’s AC 13 is shockingly low. What makes it hard to hit is its Displacement feature, which imposes disadvantage on attack rolls against it, giving it an effective AC of 17 or 18. But by the time player characters reach intermediate levels, which is when they’ll start running into foes like the challenge rating 3 displacer beast, hitting AC 17 or 18 is no longer all that difficult—a mid-level PC ought to be able to make that roll at least half the time, especially if he or she is playing smart. Since a successful hit disrupts Displacement, that means just one hit—even a lucky one—makes the displacer beast vulnerable to the next few.
Also, consider that any opponent of the displacer beast who attacks with advantage—for any reason, and even if there’s some other disadvantage in play—thereby nullifies Displacement. Unseen attacker? Nullified. Dungeon master gave you inspiration last week? Nullified. A fellow PC using the Help action? Nullified. Flank attack, if your DM is using that optional rule (Dungeon Master’s Guide page 251—I’m a fan, though some others aren’t)? Nullified. The fighter is a samurai using the Fighting Spirit subclass feature? Nullified.
So the displacer beast’s instinctive behavior set (its ape-level Intelligence 6 isn’t enough to allow it to develop new strategies on the fly) should include reactions to its taking a hit, right? Like, maybe after a successful attack on a displacer beast, the creature backs off, using its full movement speed (which will usually exceed that of any of its opponents), and waits for Displacement to kick in again?
Well, that’s what I thought at first. But a hit on the displacer beast only disrupts Displacement until the end of its next turn. Let’s look at the timing of this. Alfonso, Bethrynna, Creega and Dabbledob (thanks, Xanathar’s Guide to Everything, appendix B!) are fighting a DB. The beast has first initiative, then the PCs attack in alphabetical order. Alfonso, on his own turn, lands a hit, disrupting Displacement. Then Bethrynna, Creega and Dabbledob all get to make attacks against the DB’s base armor class.
Now it’s the beast’s turn again. It could retreat—but why? Sure, it has AC 13 for the duration of its turn, but who’s going to attack it during its turn? Nobody—unless it incurs opportunity attacks by retreating! So here we’ve got this weird situation in which what makes intuitive sense (“They found me! They hurt me! I’d better get away!”) makes the exact opposite of tactical sense (“They found me, they hurt me, but this isn’t going to make them any more likely to hurt me again, so I should just stay here and keep whapping them with my spiky tentacle-pads”).
Here we have to maintain intellectual discipline and remind ourselves that instinct arises from what’s evolutionarily successful. We also have to look at the three possible methods of retreat: Dodge, Dash and Disengage. Dodge makes no sense for the displacer beast, because its AC is low and because the mid-level PCs who’ll encounter it are likely to have Extra Attack. Dash is the most plausible, although it’s not so good when being attacked by multiple opponents who’ll all get opportunity attacks. The displacer beast’s Intelligence isn’t high enough to justify Disengage, but I do occasionally sleaze this one for creatures that have a knack for slipping away from opponents, making it a function of instinct rather than a function of discipline. Plus, Disengage is well-suited for situations in which one is engaged with multiple melee opponents (likely, in the case of the displacer beast) and/or faster than those opponents (also likely in the case of the displacer beast).
On the other hand, the fact that the melee reach of its tentacles is 10 feet, not 5 feet, means it doesn’t have to get right next to its target to hit him or her. An attacking displacer beast gets only as close to its targets as it needs to. Opportunity attacks come into play only if its opponents have subsequently closed with it. (Displacement skews the beast’s position only by “several feet,” not enough to make it appear to be in an entirely different square or hex, so don’t turn this combat into a game of Battleship.)
Here’s what it finally boils down to: When a displacer beast takes a hit, its reaction depends on whether or not its positioning, and the positioning of its opponents, confer advantage on its opponents’ attacks.
- If its opponents simply made good enough attack rolls to hit it, even though they did so with disadvantage, nothing needs to change; the displacer beast stays where it is and keeps fighting.
- If it’s engaged with a single melee opponent, and it’s being attacked without disadvantage, it moves out of that opponent’s reach (movement) toward a different opponent, which it then attacks (action).
- If it’s engaged with multiple melee opponents, and it’s being attacked without disadvantage, it uses the Disengage action, moving in such a way as to get out of reach of melee attackers, take opportunistic cover from ranged attackers, and nullify the attackers’ advantage if possible. Since Disengage consumes its action, it won’t be able to attack this turn, but it will return to the fight on its next turn.
- If it’s seriously wounded (reduced to 34 hp or fewer), it Dashes away or Disengages and moves away, depending on how many melee opponents are engaged with it, and flees the scene.
The displacer beast’s ability to analyze the reasons why its opponents have advantage against it and to respond appropriately is limited. An animal can grasp the danger of being attacked from two directions, of being struck at a distance by an attacker it can’t see or of facing a particularly ferocious foe. However, certain other sources of attack advantage, such as being limned by a faerie fire spell, will confound it. Not knowing how to respond, it will react in ways that reflect its confusion. It won’t know, for example, that it ought to consider attacking whoever cast faerie fire.
The MM flavor text portrays displacer beasts as predators that hunt for sport as well as food and that toy with their prey before going in for the kill. We can look at this as a factor that influences target selection. Displacer beasts aren’t smart, but they’re savvy enough to choose their targets well. And like all predators, their preferred targets are the young, the old, the sick, the weak, the isolated and the oblivious.
Despite the flavor text’s assertion that displacer beasts “demonstrate skill at setting ambushes,” they lack proficiency in Stealth. If this feels wrong to you, you can arbitrarily give them that proficiency (another +2, per “Creating Quick Monster Stats,” DMG 274, for a total Stealth +4) without making them unfairly powerful for their CR.
When you run a displacer beast encounter, you should choose whether food or sport is the governing motivation and have your beast(s) behave accordingly. A displacer beast hunting for sport will attack and Disengage, attack and Disengage, unless and until its opponents’ reactions force it to respond in other ways. A displacer beast hunting for food, however, will not mess around: it will attack until its quarry is dead. Moreover, once it’s reduced a target to unconsciousness, it will pick that target up in its jaws and Dash away, having no further need to stick around. (Although the rules aren’t explicit on this, I’d say it’s not slowed by the weight, because an unconscious grappled creature can’t struggle against being moved.)