“Are there unicorns in these woods? I want to see a unicorn!” Venture into any idyllic forested setting, and you’re sure to hear this request from one of your players.
Unicorns are elusive beasts—actually, not beasts, according to fifth-edition Dungeons and Dragons’ classification system, but celestials. They’re gentle, exuding a spirit of tranquility that extends to the other creatures that dwell in their vicinities, but also alert defenders of their domains. A unicorn may choose to reveal itself to a good-hearted creature, but any character who takes ill advantage of a unicorn’s good nature will be made to regret it.
I’m actually surprised and impressed by how formidable 5E unicorns are. I’d intended to draw on the suggestion I made in my earlier article on vampire tactics, about taking familiar monsters and giving them unexpected powers, and write a comical post about how unicorns could summon hordes of angry woodland creatures, disappear by running behind a tree and reappear behind another one, fire trebuchets, and rear up on their hind legs and deliver stunning roundhouse kicks like Chuck Norris. The incredible thing is, I don’t need to! Unicorns are pretty tough already.
Normally I start at the top of a monster’s stat block and work my way down, but in this case, I’m going to start at the bottom, with the unicorn’s legendary actions. That’s right—even as written, the unicorn is a legendary creature. The Hooves action allows the unicorn to make a single attack with its hooves on another creature’s turn. Shimmering Shield, which costs two of the unicorn’s three legendary actions, gives it (or another nearby creature) a +2 bonus to its armor class until the end of its next turn—given its very high Wisdom, it can easily foresee a situation in which this will be necessary, and it won’t wait until an attacker lands a hit to use it. Finally, Heal Self, which costs all three legendary actions, restores an average 11 hp, roughly one-sixth of the unicorn’s maximum hit points; it’s a suitable measure to take when the unicorn is moderately wounded (reduced to 46 hp or fewer).
As for other features, I’d been amused by the prospect of allowing unicorns to gore and trample like a triceratops—and it turns out, they already can. The Charge feature delivers extra piercing damage on a successful horn hit, and it requires the target to make a Strength saving throw or be knocked down. If you combine this with the unicorn’s Multiattack, which comprises a horn attack and a hoof attack, gore-and-trample is exactly what you get. Note that if the target is prone, the unicorn has advantage on the melee hoof attack.
Unicorns also have Innate Spellcasting. The most combat-relevant of the spells they have available are entangle and dispel evil and good, each of which they can cast once per day.
Entangle is a concentration-required area-control spell that creates difficult terrain and requires targets to make a Strength save or be restrained. The Monster Manual doesn’t indicate that the unicorn can move freely through this terrain, but it doesn’t really matter, because its base movement speed is 50 feet per round, and it needs to move only 20 feet to take advantage of Charge, so it can still attack with advantage and gain bonus damage against any target it can reach. (You may want to allow the unicorn to move through it without impediment anyway, because unicorn.) The spell’s 20-foot radius, combined with the fact that the unicorn gets to cast it only once, is a strong argument for not using it unless and until it can catch four or more opponents in the area of effect (see “Targets in Area of Effect,” Dungeon Master’s Guide, page 249).
Dispel evil and good, as I noted in the previous post on angels, is also a concentration-required spell that can be sustained to confer disadvantage on attacks by other celestials, elementals, fey, fiends or undead; or cast instantly to banish or break an enchantment cast by one of those types of creatures. Obviously, this isn’t going to do anything to a player character, so this will come into play only if a PC has summoned one or more extraplanar allies. If one of said allies has charmed, frightened or possessed an ally or ward of the unicorn, it will use the Break Enchantment option; if not, and there’s only one such ally, it will use Dismissal to try to banish it; otherwise, it will sustain the spell for as long as said allies are on the field.
Calm emotions may also be relevant, but only if a PC or party-allied NPC is casting enchantment spells on wards or allies of a unicorn. Unicorns’ at-will spells—detect evil and good, druidcraft and pass without trace—are more applicable outside combat, and it will drop them as soon as combat begins.
Aside from its hoof and horn attacks, the unicorn has two other actions that it will use primarily in defense of a creature that it’s guarding: Healing Touch and Teleport. But it can also use Teleport as a method of escape if it’s seriously wounded (reduced to 26 hp or fewer) or use Healing Touch against a moderately wounded ally if it’s not guarding anyone, or outside combat as a boon.
Along with their exceptional Strength, unicorns have high Dexterity and Constitution. The former makes them shock attackers at the start of combat, while the latter seems like it ought to allow them to keep fighting in melee like a brute. But unicorns’ AC is not very high, so they’re less durable than you might think, despite their nine hit dice. For this reason, a unicorn will Charge one turn, then Disengage (action) and run away the next, then Charge, then Disengage, and so on. Unicorns are not resistant to physical damage from normal weapons, and with their low AC, they can’t risk incurring opportunity attacks. They’ll also make extensive use of their Shimmering Shield legendary action, even though the cost might make you, as the dungeon master, leery of doing so.
Unicorns’ very high Wisdom means they’ll be careful in choosing their targets, focusing on evil foes first, then chaotic ones, and taking out ranged and melee weapon attackers before spellcasters (they can afford to, because of their Magic Resistance). It also means they won’t initiate a fight if they’re overmatched: they’ll use pass without trace to conceal themselves and their wards, and their natural speed to stay out of reach. If you’re setting up a unicorn combat encounter—because, say, the PCs are after someone a unicorn is guarding, or they’re just rotten people—you should always include enough other unicorns or fey or beast allies to make it a Deadly encounter for the party (see “Combat Encounter Difficulty,” DMG 82, and/or the Unearthed Arcana article “Encounter Building”). They’ll never flee without first making sure that anyone they’re guarding can also get away (the Teleport feature helps with this by including up to three other willing creatures).
So you’ve done all this, and it still looks like your PCs are going to kill a unicorn? You must not allow that to happen. Seriously, in that case, pull out all the stops. Have the unicorn rear up and whinny, and have three unicorns for every PC step out of the woods in a circle around the party, glowering angrily. Give them Pack Tactics and Evasion and Uncanny Dodge and Flurry of Blows and Stunning Strike. Let them innately cast conjure animals and conjure woodland beings. Have them fire bolts of radiant damage from their horns. And if you do all this and they still manage to bag one of the noblest creatures in all the realm, give them only the normal 1,800 XP for defeating a CR 5 creature. Why? Because you attacked a unicorn, you reprobates.