I often talk about undead creatures as being driven by compulsions relating to the circumstances of their reanimation, and the sword wraith is a dandy example of a backstory-driven compulsion: a warrior, obsessed with glory, slain in combat in a manner much more in line with the reality of war than the ennoblement of it, and refusing to stop seeking that glorious victory despite being technically dead. It comes in two varieties: the rank-and-file sword wraith warrior and the higher-level sword wraith commander.
According to the flavor text, despite being evil-aligned, sword wraiths don’t necessarily attack every living being who comes near. They’re closer to ghosts, haunting the locations where they met their ignominious demises and grinding their emotional axes. They can be talked to. They can be flattered. They can be offended. (Boy, can they be offended.) Mostly, they want to be treated with the adulation they expected to receive for the valorous deeds they were very sure they were capable of performing.
Both sword wraith warriors and sword wraith commanders are melee-focused brutes, with exceptional Strength and Constitution. Sword wraith warriors have animal-level Intelligence and below-average Wisdom, while sword wraith commanders have more humanoid-typical Intelligence and above-average Wisdom, so while they play the same combat role, they assess situations differently.
Both types have Longbow attacks in addition to their Longsword attacks, but they use them only under very narrow circumstances: to take potshots at fleeing enemies they can’t catch up with, if commanded to by a sword wraith commander, or if they were archers in their previous lives. (In the last case, it seems like either their Strength and Dexterity scores or their Strength and Constitution scores ought to be swapped.) The greatest glory comes from face-to-face combat, not from launching projectiles from a safe distance.
Martial Fury is a strange trait that grants sword wraiths an extra attack as a bonus action at the cost of advantage on incoming attacks. When should it choose to use this bonus action? Well, here’s the thing: The sword wraith warrior lacks the Intelligence to exercise independent judgment. Whatever it does, it does instinctually and reflexively. And given its lore, there seems to be no reason why it wouldn’t whip itself up into a state of Martial Fury all the time, even if that means leaving itself wide open to its foe’s ripostes. Its notions of physical courage overwhelm its combat sense. It makes some sense that they do, since the sword wraith warrior is also resistant to physical damage from nonmagical weapon attacks. But if someone does come at it with a magic weapon, it can’t adjust.
Should a sword wraith commander be able to exercise more control over its Martial Fury? I’d say yes except for one thing: Martial Fury seems to me to be the best mechanical expression of the sword wraith’s compulsion. A sword wraith commander may be smart enough to know that it ought to restrain its Martial Fury under certain circumstances—say, if its opponent or opponents are making more than two attacks against it in a round, following the same rule of thumb I generally use for Reckless Attack—and yet be unable to restrain itself because it’s undead. You could, as Dungeon Master, decide that the sword wraith commander can make a Wisdom saving throw each turn to see whether it can muster the willpower to do what it knows it ought to, but to me, this seems like a complication without enough payoff to justify it.
The sword wraith commander also has the Call to Honor feature, which lets it summon backup once per day. The most mathematically sensible time to do this is in round 1, but for the sake of narrative, you may wish to wait until the sword wraith commander is moderately wounded (reduced to 88 hp or fewer). However, I recommend against rolling for the number of sword wraith warriors who appear. Use a predetermined number within the given range, based on how difficult you want the encounter to be. Keep them within 30 feet of the commander, so that they can benefit from its Turning Defiance, and have them move as a tightly knit team.
With respect to target selection, sword wraiths are easily baited: they’ll engage with the nearest opponent who’s attacking them, and all other things being equal, they’ll attack the most formidable of these foes in order to prove their prowess. Sword wraith commanders have a slightly better sense of what constitutes a strategically important target and will identify, for example, a support spellcaster who’s buffing allies with a bless spell, or an Abjuration wizard projecting an Arcane Ward, as a target that needs to be taken down. Rather than leave the front line, however, they’ll direct a sword wraith warrior under their command to eliminate the asset, either by rushing them or by switching to Longbow, depending on how far off they are and how many other opponents are in the way.
All sword wraiths fight until they’re destroyed—another manifestation of their death-before-dishonor compulsion.
Next: corpse flowers.