One recent interesting shift has been more games finding a halfway point. Games which aren’t built as universally adaptable, but which share common system elements which make it easier to move from game to game. They aren’t interchangeable—often they have very different terms and sub-systems. But learning one game makes playing others easier—you could argue this for Powered by the Apocalypse, Forged in the Dark, and the Mutant System. There’s no generic version to work from, just an SRD in some cases.
Modiphius’ 2d20 engine falls into this category. It’s one I’ve come to appreciate over the last couple of years. I’ve run three different 2d20 rpgs: Conan, Star Trek, and Dune. At first I wasn’t sure about it, but the more I’ve played the more I’ve come to appreciate and enjoy the system. I like how the designers have changed things for each iteration—simplifying over time but then layering back in complexity when it fits the game.
- Mutant Chronicles 3rd Edition
- Robert E Howard's Conan
- Star Trek Adventures
- John Carter of Mars
- Dune: Adventures in the Imperium
- Fallout 2d20
- Achtung Cthulhu! 2d20
In this post I’m going to walk through the 2d20’s basics, the most common elements shared across these games. On the one hand, this should give you a sense if this is one you’d be comfortable with. On the other hand, I hope this will provide a primer to make it easier to pick up and get any of these. This post presents a simple overview with the broad sweep of mechanics, but it may not be exactly what goes on in any particular game.
Some of these versions have more detail and “crunch” (Conan, Fallout) while others are easier and more streamlined (Dune, Dishonored). In a follow up post I will walk through each of these to talk about what they offer and how they differ. But this post focuses on shared mechanics.
Characters generally have two pools of ratings. While these use different terms, we’ll refer to them as Attributes and Skills. That’s how Conan approaches them. Star Trek has Attributes and Disciplines, Dune has Drives and Skills, etc.
The range for these ratings varies from game to game. In some games there’s an emphasis on Attributes (Conan) with skill numbers being much lower. Others, like Dune, have relatively balanced values between the two sets of ratings. Another different can be the actual number of ratings. For example Star Trek & Dune have the same number of attributes as skills (six and five respectively). Earlier games like Conan and Mutant Chronicles have a small set of attributes and a larger pool of skills.
The key idea here is that when you attempt a task, you determine which attribute and skill combination you’ll be using to roll. That total gives you a target number. In some versions which pairing you use is based on the situation and player negotiation. In others, like Fallout 2d20, any task has a set combination.
When characters (PC or NPC) attempt a task, the GM sets a difficulty—the number of successes a character needs to succeed. Other factors can impact this difficulty, but let’s stick with this for the moment. Usually this will be 1 or 2. If it’s an opposed test, both sides roll and compare successes.
Players roll 2d20. Each die which rolls under the target number counts as one success. A “1” on a die counts as two successes. Rolling a 20 is failure and also creates a complication. Certain circumstances may increase this complication range.
Each game has a mechanic for focuses or specializations. If you have a focus which fits with the task you’re attempting, you increase your critical success range. For example in Star Trek if you have a focus then any roll of 3 or less is two successes. In Dune if you have focus, then any roll equal or less than your Skill counts as two successes.
The base system has a few other wrinkles. Certain talents and a spendable resources may allow rerolls at this point. For example Determination is a currency in ST which can be spent for a reroll if it matches a character’s Drive. Other talents allow players to ignore complications, reduce the difficulty, and so on. To aid someone, the assisting player rolls a single d20 with their relevant attribute + skill and add any successes to the total.
One of the most important aspects of 2d20 is the idea of Momentum. For every success you get which is greater than the difficulty of the test, you generate a point of momentum. This can be spent immediately on effects. For example you might ask additional questions or do more damage. On the other hand, you can also opt to put momentum into the group pool. Any player may draw from this pool later, usually to power talents or add more dice to a roll.
What you can do with momentum varies from game to game. Usually the more detailed or crunchy a game, the more elaborate the momentum spend options. For example, Conan has both standard and combat options for momentum. Here’s just the combat side: (Numbers listed below indicate momentum cost and an R means you can do it repeatedly.)
- Bonus Damage 1 R A character can increase the damage inflicted by a successful attack, regardless of the type of attack. Each Momentum spent adds +1 damage.
- Confidence 1 R The character gains 1 Morale Soak per Momentum spent (maximum 4) until the start of his next turn.
- Disarm 2 or 3 One weapon held by the target is knocked away and falls to the ground within Reach. This costs 2 points of Momentum if the target is holding the weapon in one hand or 3 Momentum if the weapon is braced or held in two hands.
- Penetration 1 R The damage inflicted by the current attack ignores an amount of Soak equal to twice the Momentum spent.
- Re-roll Damage 1 The player may re-roll any number of damage dice from the current attack
- Second Wind 1 | R The character recovers 1 point of Vigor or Resolve for each Momentum spent.
- Secondary Target 2 A second target within Reach of the primary target is also affected by the attack, and suffers half the attack’s damage, rounding down.
- Swift Action 2 The character gains an additional Standard Action, increasing the difficulty by one step on any skill test that action requires. This may only be done once per round.
- Withdraw 1 The character leaves the Reach of an enemy, without triggering any Retaliate Reactions.
On the other hand, Dune has only a handful of uses for momentum: buying additional d20s for a test, creating a temporary trait, acquiring an asset, obtaining information, or activating certain talents.
The GM also has a parallel set of points. These are Dark Symmetry in Mutant Chronicles, Doom in Conan, Threat in Star Trek and so on. The GM can spend these for extra dice, additional effects, etc. “Doom” can come from several sources, but most importantly a player may opt to take Doom to temporarily generate Momentum (usually to get a reroll or extra die).
One of the biggest differences between 2d20 versions is whether they use effect dice. So far all but Dishonored and Dune use these; John Carter uses standard d6s. Those two take a different approach to measuring damage, impact, and resistance.
Effect dice are d6s with four results. The number rolled is usually based on the equipment or attack involved (weapon, armor, spell type). Momentum can usually be spent to add extra dice to the effect on a success.
- 1: Shows a 1, meaning one wound, damage, or success.
- 2: Shows a 2, meaning two wound, damage, or success.
- --: Two sides show blanks meaning that no damage or success occurs.
- *1: Two sides show the special effect symbol as well as a 1. The symbol varies from game to game, which is how you get different collector’s versions, but the dice are interchangeable between games. The 1 here means one wound, damage, or success. But the special symbol means that additionally you may trigger an Effect depending on what you’re doing.
The effect die is cool, but does require special die mapping for online play. You could read them as a normal d6 (with 3,4 being blank and 5,6 being 1+effect), but that’s an extra step of reading an mental calculation which can get irritating after a while, especially with big pools of dice.
One innovation which appears from Star Trek (I believe) forward is the idea of Traits. Traits can be applied to anything—people, locations, tools, etc. When relevant these can be used to change facts about the situation or change the difficulty of a task. Imagine these like Aspects from Fate. Dune, in particular, leans heavily into traits and assets (which function like a particular kind of trait).
Each 2d20 game has its own take on these mechanics. For example, damage is handled quite different ly between games, as is initiative, movement, etc. In the second part of this series, I’ll take a look at each of the 2d20 games to go through those differences, what sub-systems they bring into play, and how they tune the system to emulate the setting.
Other System Guides and Overviews
Age of Ravens: Fate System Guide for New Players (Part One)
Age of Ravens: Worlds of Adventure: Fate Guide (Pt. 2)
Age of Ravens: Legacy: System Guide for New Gamers
Paragon System: Glory and Agony