The Harlequin's Kiss and other Xeno filament weapons currently lack the proper mechanics used in previous versions of 40K (particularly 2nd Ed). The deadliness of the HK was its elegance. The HK was deadly to its user because it injects a rapidly spinning monomolecular wire into the target, ignoring toughness, and turning the creature into goo. Since it was so thin it never "penetrated" armor, that too is an inappropriate mechanic. The fine, tensile wire is capable of working into the "flaws" of armor and damaging the softer innards, which is why Harlequins use Refractor Fields.

House Rule Harlequin's Kiss:

Damage 1D10*

Pen 1D10**

Tearing

* Do not add user's strength to the attack. This damage ignores Toughness.

** Add user's strength to the Penetration value, rolling separately for each individual attack.

Filament Grenades:

Damage 2D10*

Pen 1D10**

* This damage ignores Toughness.

** Roll separately for each creature hit.

On a related topic, Warp Spiders use a "Flamer" that mimics the Filament Grenade but uses a single die for damage. I'm currently converting some 40k favorites so the characters have more Xenos to fight.

Doesn't this mean that unless Righteous Fury shows up, the Kiss is generally unable to one-shot-kill a healthy human? That seems a bit weak to me compared to power weapons, chain weapons, and even (my personal favorite) the mono groxwhip. Sure, it probably has excellent AP, but that only matters up to a point - anything past AP 8 (or so) is wasted effect in most cases.

OP's house rules nerf the HK pretty badly. Ignoring Toughness does ream Orks and the like pretty badly, but I'll take 1d10+8 damage and Pen 10 over 1d10+SB and 1d10+SB Pen any day. Also weirdly contradictory. Harlies (indeed, all Eldar) aren't noted for having high SBs to begin with, and you'd need a Strength of 40+ to make his version of HK even on par with the real one.

Argoden said:

It's worse than that - the damage proposed is just 1d10, there shouldn't be a "+SB" in there. That's really poor damage for such a deadly weapon.

HappyDaze said:

Urg, you're right. Total nerf.

Perhaps a Harlequin killed his dog or something?

He should probably nerf the mono enhancement as well then, since FFG and Black Industries before that pretty much set the bar at mono- better armor pen. He's also reacting from a flawed viewpoint of how the Kiss works. It's not the monofilament wire that penetrates the armor, it's the HK itself (the metal tube used for "injection") that penetrates the armor, then unleashes the wire inside of it, causing the creature's armor to become its deadly prison as the wire whips around inside of it turning the being into soup. The Harlies kiss in the tabletop game works in pretty much the same fashion.

The DeathSpinners (monofilament flamers) that the Warp Spiders use, tabletop style, come with incredibly high strength value (doing damage akin to the assault cannon) with no armor pen (to represent that the wire itself doesn't have any armor punch capability, but it could worm its way through imperfections in the person's armor).

To stay true with how I remember the dreaded Harlequins Kiss from 2nd edition 40k (when strange weapons still had individual rules) I'd suggest something like:

Harlequins Kiss : Melee, Damage 4d10, Pen 1d10-3+SB. Unholy xenos monofilament weapon*

Deathspinner : Basic, R:20m, damage 4d10, pen 1d10. Flame, Unholy xenos monofilament weapon* A set of twinlinked deathspinners (common with the warpspiders) will fire as one Flame weapon but will count their penetration roll as Tearing.

New weapon special quality:
Unholy xenos monofilament weapon : This weapon will do damage only if the penetration roll beats the targets armor value on the location that was hit. It will always apply its damage to the Body location, no matter what location was hit and penetrated. Fury of the Emperor will only happen on the penetration roll, rather than on the damage roll. Abilities that grant extra damage will be applied to the penetration roll, rather than to the damage roll. Abilities that grant extra critical damage will not effect this weapon, due to it's random nature.

New xenos Talent:
Aim for the joints . Requires training by pansy-dansy eldar harlequins or in a similar fighting style. Requires Agi 40, Per 40. You are trained to find the weak spots of your opponents armor such as joints and visors and to move and direct your blows to maximise their vulnerability. All your melee strikes, unarmed or using onehanded weapons, gain +3 Armor penetration. Cannot be combined with the Mighty Blow talent or any weapon with the Flexible special quality, due to the precision needed.

These weapons will average 22p of damage (with no possibility of fury, despite all the dice rolled), if they penetrate the armor. Quite enough to badly hurt a regular human. Penetration of the HK will be on average 8.5 for a harlequin (Aim for the joints and SB3) min 4, max 13 + chance for fury of the wraithbone(?). In the hands of a competent human fighter it will average 9.5 (SB5 and Mighty Blow) min 5 max 14 + chance of FotE. A weapon that is mostly useful against medium to lightly armored enemies, but still have the possibility to kill Powerarmorwearers or burst through a badly fitted hatch to a battle tank. Penetration of the Spinner will be an average of 5.5, or 7,5 with Mighty Blow.

Lets compare the HK to the Power Sword. The same human fighter as above, SB5 and Mighty Blow (+2 damage). Hitting a target in Power Armor (AP8) first with the kiss, then with the Mordian powersword (D:1d10+5, Pen:5).
With HK: 60% chance to penetrate the armor, so an average damage of 0.60*22=13.2
With Powersword: Average damage 17.5, pen 5. So average damage 14.5.

Against a target in guard flak (AP4) or less:
With HK: 100% chance to penetrate the armor, so an average damage of 22
With Powersword: Av damage 17.5

Against a target in Marine Power armor (AP12 on body)
With HK: 20% chance to penetrate the armor, so average damage of 0.20*22=4,4
With Powersword: Av damage 17.5, pen 5, so av effective damage of 10,5
Interesting thought, a Powersword will deal little damage through the unnatural toughness of a marine, while a HK will certainly make an impression on the hits when it breaks through the armor.

This means that against most medium to soft targets the HK beats the Powersword wich is just as it should be, this is a highly illegal, exotic-talent-needed, Extremely Rare melee weapon from one of the most skilled fighting cultures in the galaxy. I would consider giving the HK an extra d10 for damage, that would upp average damage against the guard flak to 27.5, against the ap8 PA to 16.5 and against the marine armor the average would be 5,5. In that way it would actually be better than the (posssible starting equipment) power sword, even against power armored enemies. I'd say ajdust it as it would fit your story. These rules also makes for interesting thinking around unnatural strength and similar, wich is always a good thing. I think it makes for a meaningful choice for a rare and interesting piece of equipment.

Suggestions and feedback would be greatly appreciated.

It's not just the joints that the wire goes through. Back in 2nd ed the wire from a deathspinner had a -2 save modifier. It slaughtered everything. You rolled against the targets' initiative, gaining +1 for them being completely covered by the template (because back then a deathspinner used the HEAVY FLAMER template, which as we all know is larger than the current flamer template). If you hit them and they failed their armour saves they died, regardless of wounds. The harlequin's kiss in 2nd ed simply killed you if you failed an armour save after being hit, although it didn't have an armour save modifier like the deathspinner.

Now, being a single monofilament wire, it should be able to move between the molecules of the target's armour and flesh as well.

What I'm thinking is:

Monofilament

A weapon with this quality treats all armour as Primitive and receives the Tearing quality. SB is never added to a monofilament weapon's Damage. Damage is reduced by Agility Bonus instead of Toughness Bonus.

Harlequin's Kiss melee, Damage 2D10+5 R, Pen 2 Monofilament

Deathspinner: Basic, R:30m, Damage 3D10+5 R, Pen 4, Clip -, Reload -, Special Flame, Monofilament

Xeno Filament grenade: Thrown, SBx3, Damage 4D10+5 R, Pen 4, Blast (1), Monofilament

So what you ahve is a weapon whose only defence is to have fast reflexes to avoid the worst of the attack. Which seems to be what the original design intent is supposed to be.

Note also that the deathspinner never needs reloading as it doesn't shoot any ammo, it's like a magnetically contained whip that retracts after use. However the larger support weapons do release clouds of free floating monofilament nets so they would run out of ammo.

Hellebore

Alternatively monofilament weapons can do automatic CRITICAL damage, which means they can kill you very quickly. ie a harlequin's kiss does 1D10 critical damage, if you roll a 8+ you've pretty much killed them in one hit. You would only have to hit them twice to kill them on average.

Very nasty though.

Hellebore