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The Cthonversion Kit is a way of adapting d100 games to the Mork Borg hack: Cthork Borg

It's a single page and designed for on-the-fly conversion, allowing you to run adventures and campaigns from the greater d100 scene with Cthork Borg.


MÖRK BORG Third Party License - Cthonversion Kit is an independent production by Richard Kelly and is not affiliated with Ockult Örtmästare Games or Stockholm Kartell. It is published under the MÖRK BORG Third Party License. MÖRK BORG is copyright Ockult Örtmästare Games and Stockholm Kartell. For further details about the MÖRK BORG Third Party License, see https://morkborg.com/license/



  • 4/4/22: Fixed skill conversion, clarified spell casting, reorganized and clarified language throughout
  • 5/15/22: Clarified rules for NPC skill use as well as opposed rolls against NPCs.
CategoryPhysical game
Rated 5.0 out of 5 stars
(5 total ratings)
GenreRole Playing
Tags1920s, cthork-borg, Horror, mork-borg, Survival Horror, Tabletop role-playing game


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Click download now to get access to the following files:

Cthonversion Kit 5.15.22.pdf 64 kB


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(6 edits) (+1)

Hello!  Quick question on converting d100 NPC/monster percentage values: how does this work in play?  

For example, if I have a night watchman with 65% Spot Hidden, this becomes 13 in Cthork Borg (1 DR per 5% skill rating).  Subtracting 13 from 20 is DR7.  So the night watchman has a Spot Hidden DR7...IF the night watchman NPC is the one doing the rolling.


Since in Cthork Borg, the player-characters are typically doing the dice rolling most of the time, DR7 seems awfully low for them to elude the night watchman with Spot Hidden 65%.  By the same logic, a night watchman with Spot Hidden 75% would have a DR5, and be even easier for the player-characters to elude, if we're subtracting the watchman's value from 20.

In other words, why subtract from 20?  Why not just take the NPC or monster's percentage value and divide it by 5 to get the Cthork Borg DR value?

If the NPC or monster is making the roll, then yes, subtracting from 20 makes sense. 

Thanks and best,

Brian C., avid Cthork Borg fan

Ah, okay. This might be a design problem with no perfect solution.

In Cthork, with player vs NPC rolls, you typically just have the player roll against standard difficulty (DR 12). You can also apply penalties or bonuses based on weather conditions, the skill of the opposition, etc.

Those 'subtract from 20' values are for if an NPC needs to use a skill on their own. For example, Spot Hidden on a dingy room, or Climb up a cliffside.

That said, calculating 1 DR for every 5% of the NPC's skill definitely also works, and your method gives a lot more nuance to opposed rolls. I think GMs could use either.


Basically, in your above example, the Night Watchman's Spot Hidden DR 7 isn't the difficulty for players to sneak past him. It's the difficulty for him to spot non-player things in his environment. If he does try to spot a player, the roll for the player to sneak past him is DR 12 + optional modifiers assigned by the GM.

I figured out a better way to phrase this and patched the document!

The current version, 5.15.22, should resolve the issue.

Wonderful!  Thank you!

No problem!