The Haunted Knight is an empty suit of armor that holds the corridors of The Collapsed Kingdom, the Legendary Monsters ruin buried under ordinary Forest and Plains. It stands up and swings the moment you get close, and killing one gives you the advancement called Living Armor, which is a fair description of what you’re fighting.
They only carry 50 health and 5 armor, so on paper they aren’t much of a wall. What makes them different is the parry, as a hit landed at the wrong moment does nothing at all and gets answered with a heavy counter. Working out when to swing is most of the fight, and the Possessed Paladin will test the same lesson on you later.
Spawning
Haunted Knights don’t spawn naturally in any biome or at any light level, so waiting in the dark will never produce one. Every one you’ll meet is placed when The Collapsed Kingdom generates, and they’re all marked persistent, so they won’t despawn while you’re away and they won’t come back once killed. The structure switches off natural monster spawning inside its bounds too, so a room you cleared stays cleared.
The ruin generates about 110 chunks apart across those biomes, so you won’t be tripping over one every other ride out. Biomes O’ Plenty and Oh The Biomes We’ve Gone add a few more biomes to the list if either is installed. That spacing is wide enough that the locate command beats riding out and hoping.
Each Knight wears one of three sets of armor, Iron, Gold or Diamond, and which one it gets is fixed when the structure generates rather than rolled as you walk in. The armor makes no difference to its health, its damage or the way it fights, it only decides which metal you get back. Most of the ones down there are wearing Gold.
The trail its sword leaves matches the armor as well, pale gray for Iron, yellow for Gold and a light blue for Diamond, so you can tell what a room is worth before anything dies. A Spawn Egg rolls the armor at random instead, so the trail is the only tell you get there.
Behavior
A Haunted Knight will come for you as soon as it can see you from about 18 blocks, and it goes after 
Iron Golems and 
Snow Golems too. It treats every other Collapsed Kingdom monster as an ally, so its sweeps pass straight through the Haunted Guards beside it and you won’t be turning them on each other.
Attacks
Everything it has is the same sword swung in front of it, and both openers lunge a short way toward you first, enough to close a gap you thought was safe. The single slash lands about three quarters of a second after it starts. The spin is two sweeps roughly a second apart, each one cutting a wedge of about 100 degrees out to two and a half blocks.
Slash
Spin
Parry Counter
Only one thing beside your actual target gets caught, so a pet standing next to you isn’t in as much trouble as it looks. None of it reaches more than about 3 blocks above its own feet, so a pillar takes you out of the fight entirely if a room goes badly. It also shrugs off most knockback, so a sword with Knockback on it won’t buy you much space.
The Parry Stance
Rather than attacking, it will often plant itself and hold the sword up, waiting to be hit. Anything that lands while the guard is raised gets refused with the same clang a 
Shield makes, and a counter comes back for it, which is where most deaths in this structure come from. It only gets the one parry per stance, so once the counter is spent the stance is over.
Guard Up
It stops and lifts the sword
It breaks off whatever it was doing, roots itself in place and raises the blade in front of it. The parry isn’t live for the first fraction of a second, so a swing that’s already on its way through will still land normally.
The Window
About 1.4 seconds
For the next second and a bit, anything that reaches it is refused outright and it won’t take a single point of damage. 
Arrows count here as well as melee, so a shot fired to be safe still feeds the stance.
The Counter
13 damage and a Stun
The counter sweeps a full 180 degrees around it for 13 damage out to two and a half blocks, catching up to four other things at the same time. It also puts Stun on you for three quarters of a second, which roots you, slows your swing and drops whatever you were holding up, so even a blocked counter leaves you wide open for the swing after it.
The Whiff
About half a second open
If nothing hits it, the stance runs out on its own and it spends about half a second recovering with the sword down, taking damage normally. That’s the cleanest opening in the fight and you get it free every time you decide not to take the bait.
The counter is the hardest hit it has and it lands with a Stun attached, which is what turns one mistake into two. It lunges before it swings, so backing off a step isn’t enough. If you see the guard go up, get well clear and wait the second out, or break the stance with a 
Bow from further back where the counter can’t follow.
That whole sequence takes under 3 seconds from the guard going up to the recovery ending, so it’s over before most players have decided what to do. Watching it once from out of range teaches you more than trading with it does.
Weaknesses and Openings
There’s a second window where it can’t be touched, and it’s much easier to miss. From the moment it begins a single slash until just before the blade lands, it takes no damage at all, so a trade you thought you won was really you hitting a wall. Between that and the parry, most wasted swings in this fight land on a Knight that simply wasn’t hittable.
A Bow gets around both of them, as the counter only reaches about two and a half blocks and anything fired from further out burns the stance for nothing. It won’t swing or plant a stance at all unless you’re inside about 3 blocks, so shots from further back are free. Past those windows it has no immunities, so fire, Potions and every enchantment work the way you’d expect.
Drops
The 
Knight’s Sword Blade Half is the reason to clear these rooms, as two halves and a 
Stick give you a 
Knight’s Sword. It drops glowing and hangs around far longer than a normal item does, which saves a lot of squinting in a dark crypt. A single half can also be turned back into one 
Iron Ingot, for the odd one you’re left holding.
Haunted Knight Drops
Knight's Sword Blade Half 
Gold Ingot 
Iron Ingot 
Diamond The sword adds 5 attack damage for 6 in total, swings at 1.7 and carries 250 durability, repairing with Iron Ingots. Beyond being a weapon it’s the base of the 
Knight Summoner, with a 
Corrupted Soul from the Possessed Paladin and 7 Iron Ingots, so you’ll be back for it once the boss is down. That summoner hands you a tamed Knight, covered in Companions & Summoned Allies.
The metal alongside it is pure armor luck, and the Diamond ones are the exception in that they might give you nothing at all. None of these drops are affected by Looting, so there’s nothing to gain from swapping weapons before the kill.
Tips
Keep your Shield up, because it genuinely works against this one. The Haunted Knight has nothing in its kit that breaks a block, unlike the Haunted Guard standing next to it, whose slam disables your Shield for 5 seconds. The one thing to watch is the Stun on the counter, as that drops your guard for three quarters of a second whether you were blocking or not.
Pull them into a doorway when a room has two or three, since each sweep only catches one thing beside its target and nothing can flank you in a corridor. Deal with the Haunted Guards first when they’re mixed in, as they hit for 14 in a full 180 degree arc and carry twice the armor.
Two swings, then out, is a loop that works on every one of them. Back off the moment the sword comes up, then step back in for the recovery. You give up a little damage per cycle but you never feed a parry, and with 50 health to chew through you’ll still get there quickly enough.
FAQ
There are no natural spawn rules for them at all, so no biome, light level or difficulty will produce one. Every Haunted Knight is placed when the structure generates, and they’re persistent, meaning they stay put until you kill them and never come back afterward. Outside of that the only way to get one is the 
Haunted Knight Spawn Egg.
You’re hitting one of its two invulnerable windows, and the clang is the tell for both. The first covers the windup of its single slash, until just before the blade lands, and the second is the parry stance, which lasts about 1.4 seconds and answers with a counter. Wait for the sword to come down, or for the half second of recovery after a parry, and your hits land.
Two of them stacked above a Stick craft the Knight’s Sword, which gives 6 attack damage at 1.7 speed with 250 durability. The sword then tops the Knight Summoner recipe with a Corrupted Soul and 7 Iron Ingots, so keep the halves even after you have one. A spare half breaks down into one Iron Ingot if you end up with an odd number.
Not in the slightest, as all three have the same 50 health, 5 armor and the same attacks. The armor only decides the metal it drops on death, which is 2 to 5 Iron Ingots, 2 to 6 Gold Ingots or up to 2 Diamonds. A Diamond one might give you nothing, so the iron and gold ones are the steadier return.
