Converting Dark Heresy 2 to D&D 5

As mentioned in previous posts, we’re trying to rebuild our buffer so that we can get through convention season alive. This means we’re doing a lot of Vestitas, but many Vestitas encounters can be converted into D&D 5e encounters. In this post, we will briefly explain how.

Vestitas encounters tend to be isolated and remote from one another. Other than the ones with overt technological themes that place them squarely in the grim darkness of the far future (like the Wolf Brother), they can be dropped into a D&D campaign with almost no editing at all. The problem is the math, but fortunately that problem is solvable.

So, Dark Heresy 2 runs on a d100 roll under system while D&D 5e runs on a d20 roll over system. The mathematics on this are a lot simpler than you might think. Every 5 points in DH2 is 1 point in D&D 5, and higher difficulties add to the DC instead of subtracting from the player’s roll. You can even use this to convert DH2 to a d100 roll over system without changing any rules or balance at all. The target number is always 100, and if you beat 100, you win. Your characteristic, skill, and difficulty modifiers are added to your roll rather than the target you’re trying to roll under. So, if you’re making a shot at BS 35, you add 35 to your roll, which means you need to roll 65 or higher to succeed, which is exactly the same likelihood as rolling a 35 or lower. It’s the same if you add 30 for firing at point blank range so your total is now 65, which means in roll under you need to roll 65 or under and in roll over you need to roll 35 or higher and those are almost exactly as likely as one another. This can make counting degrees of success or failure easier, too. 100-109 is always one degree of success, 110-119 is always two, and so on. 90-99 is always one degree of failure, 80-89 is always two, and so on.

Technically, in order to have the math be exactly the same, your success should be at 101, because the minimum roll on a d100 is 1, not 0. So your first degree of success would actually be 101-110, and two would be 111-120, and for degrees of failure it would actually be 91-100 and so on. The difference is of 1%, which is so tiny that it almost never comes up, and it’s a bit cleaner to be able to say that all of the 90s are one degree of failure, and to have the target number be a nice round 100.

Once you’ve converted Dark Heresy 2 to roll over, you can convert that to d20 by just dividing things by 5. Also, you now add difficulty to the DC instead of subtracting it from the die roll. Of course, just because you’re using the same RNG doesn’t mean you’re using the same math. D&D 3, D&D 4, and D&D 5 all use the same basic system, but the numbers are radically different. D&D 3, for example, has higher DCs and higher bonuses than D&D 5 across the board and especially in the end game. Dark Heresy 2 characters start with bonuses as high as 50, which is a +10 when translated literally into d20, and their worst stats tend to be between +1 to +3. D&D 5 characters, on the other hand, range from -1 to +5 at start. Dark Heresy characters’ skills cap out in the neighborhood of 85, which is a +17, whereas D&D 5 characters max out at +11 (we’re not counting expertise here, since that’s a specific and uncommon class feature). DH2 is usually about five points lower, so in order to convert, you’ll want to decrease the DCs by 5.

So here’s a handy chart:

Very Hard(-30): DC 21
Hard(-20): DC 19
Difficult(-10): DC 17
Challenging(+0): DC 15
Ordinary(+10): DC 13
Routine(+20): DC 11
Easy(+30): DC 9

Combat stats don’t translate so easily, especially in terms of wounds. High threat creatures in DH2 have wounds about five times those of starting baddies, but high challenge monsters in D&D 5 have HP about fifty times those of starting baddies. It just doesn’t compare. Even when we do start making Vestitas bestiary posts, it will regrettably not be of much help to those running 5e encounters. Fortunately, the Monster Manual (and, we assume, Volo’s Guide to Monsters) is quite extensive and you can probably find comparable monsters to use for your encounters.


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