These stats are really an artifact from 2020; I wrote them up when I first cracked open Perlesvaus that summer. I haven't been statting up stuff from our texts as much lately, but if that's content y'all want, do let me know and I'll make more of it happen.
Anyhow, here is a creature inspired by King Arthur's encounter with a Black Knight near the beginning of Perlesvaus. The stats are for Pathfinder 1e; feel free to convert as desired. (And if you do, let me know, and we can share the conversions for other players of whatever your favorite TTRPG is.)
The creature in question is, of course, our Ant Knight. As you may recall, this is the fellow who attacked King Arthur outside the Chapel of St. Augustine, then after his death, was dismembered and hauled off by his comrades, which is why I started calling them the Ant Knights. In this interpretation, they are literally humanoid ants.
Myrmex
CR 7; XP 3200
Lawful Blue* Medium Fey
Init +2; Low-Light Vision; Perception +13
Defense
AC 23, touch 12, flat-footed 21 (+2 Dex, +2 shield, +9 natural)
hp 68 (9d6+36)
Fort +7, Ref +8, Will +7
Defensive Abilities: Bravery +3
Offense
Speed 30 ft.
Melee: Masterwork lance +11 (1d8+5/x3) , longsword +5 (1d8+5/19-20,x2)
Spell-Like Abilities (CL 9; concentration +11): Phantom Steed 3/day
Special Attacks: Powerful Charge (lance, 2d8+10)
Statistics
Str 21, Dex 14, Con 18, Int 10, Wis 12, Cha 14
Base Atk +4; CMB +9; CMD 21
Feats: Greater Bull Rush, Improved Bull Rush, Improved Natural Armor, Martial Weapon Proficiency, Mounted Combat, Power Attack, Ride-by Attack, Spirited Charge, Weapon Focus (lance), Weapon Focus (longsword)
Skills: Handle Animal +11, Intimidate +11, Knowledge (local) +12, Perception +13, Ride +11, Survival +10
Languages: Common, Sylvan
Special Abilities
Powerful Charge (Ex) : When a Myrmex makes a charge, its lance attack deals 2d8+10 damage in addition to the normal benefits and hazards of a charge.
Bravery (Ex) : A Myrmex gains a +3 bonus on will saves against fear.
Never May You Be Heal Thereof (Su) : Any melee damage done by a Myrmex cannot be healed unless Myrmex blood is applied to the wound. Once said blood is applied, the wound heals twice as quickly as usual.
Right Foully Hath It Come True (Su) : A wound delivered by a Myrmex in a dream will appear on the sleeping body of the dreamer as if delivered in the waking world. At the GM's discretion, when a Myrmex is encountered in Dream, other items or effects from the dream world may also bleed over into waking life -- e.g., an item held in the dream may still be in one's hand when one awakes.
Ecology
Environment: Dream
Organization: multitude (6-36)
Treasure: standard (incl. masterwork lance, longsword, & heavy shield)
* The Fae are neither good nor evil. In assigning alignment to them and creatures of the Far Realms, I borrow terminology from TV Tropes: Blue and Orange Morality. The Fae are blue; the Far Realms are orange.
The Myrmex are fae warriors, black-armored and foul-favored, who resemble anthropomorphic ants in plate mail. (The plate mail is, in fact, just their exoskeleton.) Encounters with a Myrmex typically take the form of a challenge to duel as a result of some wrong you have done, real or imagined. Though a Myrmex is never alone -- even if they appear alone, their companions are hidden nearby -- it will typically fight alone, following the rules of a chivalric duel. The companions will not get involved unless the Myrmex's opponent violates the appropriate conduct of a chivalric knight; as long as the opponent follows the rules of the duel appropriately, it will remain a duel, but if the opponent cheats or calls in help, the whole multitude of Myrmeces will ride out of the forest -- or possibly through the veil of dreams -- and intervene. It should be noted that a Myrmex duel is not typically to the death; they will surrender if they feel they are beaten and will accept your surrender honorably.
Myrmeces are inhabitants of Dream more often than the waking world; initial encounters with a Myrmex are more likely to occur in one's dreams than in waking life. As far as Myrmeces believe, the two are more or less equivalent -- if you meet one in your dreams and wrong it somehow, the resultant duel may well take place in the waking world once it catches up to you. (Assuming it did not manage to deal with you there and then in Dream.) They are capable of travelling through the veil that separates Dream from the waking world as easily as you would walk through a doorway, though it might take a few days* for them to determine where you are in the waking world in order to direct their travel properly.
If you slay a Myrmex honorably -- i.e., its opponent does not in any way cheat in their duel -- the other Myrmeces with which it travels will wait for them to back off a little ways, then appear from Dream, dismember their fallen comrade, and carry off the pieces. This odd behavior is part of their funeral custom, but is also somewhat spiteful -- collecting the body in this way removes any possibility of their opponent healing their wounds using Myrmex blood. They are fastidious and thorough in this -- once they are done with this process, there will not be sufficient blood remaining for use.
*Note for GMs: the following is my recommendation for how to time this. If a player wrongs a Myrmex in Dream, roll a d12. If at any point in the next [d12] days the PC is capable of fighting a duel (i.e. fully healthy, within reach of their arms and armor, not otherwise engaged in battle, etc.) but it would be deeply inconvenient for them (e.g. they are at a high-society ball), that is when the Myrmex steps through the veil of dreams to appear in front of them and demand immediate satisfaction. If the [d12] days pass without any such opportunity appearing, the Myrmex simply arrives when the time runs out.