First off, Powered by the Apocalypse is not a system, it's a design style. I put hallmark PbtA design characteristics in three categories:
- Elements that are the same as any traditional or old school RPGs
- Elements that differ only in terms of mouth feel
- different names for things (e.g. stat vs. attribute)
- minor mechanical differences (e.g. 2D6 vs. d20 vs. 1d6+modifier)
- Significant structural or role differences from traditional RPGs
First of all, as with most traditional RPGs, play is free-form unless the rules apply: players say what their PCs do, the GM says what happens in response.
Many rules follow a standardized format that looks something like this:
When you attack an enemy in melee, roll 2d6+Str.
- On a 10+, you deal your damage to the enemy and avoid their attack. At your option, you may choose to do +1d6 damage but expose yourself to the enemy’s attack.
- On a 7–9, you deal your damage to the enemy and the enemy makes an attack against you.
Player-Facing Rules
More significant is that most rules are written to be player facing. Much like combat in the old Fighting Fantasy books, monsters don't roll dice when they attack you; the player is the only person rolling dice during melee.
This is a bit like rules for wandering monster movement in B/X D&D—there aren't any. While player food, light and movement through the dungeon are all tracked meticulously, all of that is hand-waved for monsters.
Monsters (or townspeople) just appear when a wandering monster roll says they should, and nobody worries about their precise location before that. Their precise inventory doesn't matter either, not until they're dead and examined more closely.
Until it actually matters, most of this stuff is completely undefined, held behind a "curtain of vagueness," until it matters.
PbtA games take this same approach, but the "curtain" is a bit closer to the PCs. There are no rules for NPCs to jump over things, persuade people, or to hit or shoot things—the rules only come into play when they try those things on a PC. In other situations, the GM just decides what happens.
GM Moves
Speaking of the GM, one obvious hallmark of PbtA games is the so-called "GM Moves." These look like a set of rules, but they're basically sensible GM advice encoded as a set of imperatives. Many PbtA games do say that the GM should only use these moves, but jointly they're so broad as to be all-encompassing.. so it's no restriction at all.
Here are a few of the GM moves from The Regiment, which is a World War II RPG:
- Announce impending danger
- Separate them
- Inflict fire (as established)
- Introduce news from home or other fronts
- Remember: gear can fail
- Corner them
- Capture someone
- Make them buy it (supply, gear, smokes)
- ...
Now, some people will crow that restricting the GM to these moves are rules and furthermore, that they somehow make the game more fair, taking arbitrary fiat and the potential for abuse out of the GM's hands!
Ignore these people—in my opinion, they're expressing an attitude toward authority that has nothing to do with the game, just like the grognard nincompoops that assert that the DM is somehow the father figure of the play group.
To my mind, encoding GM advice as "GM moves" is a mouth feel difference, not a meaningful one that makes the game something new. It is, however, a concise and useful format, and a good way to highlight important genre differences.
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Now for some meatier differences! Not all PbtA games have these things (so they're not necessarily inherent to the PbtA design approach), but they're common enough that they're worth mentioning.
Ensemble Cast
Many PbtA games are very much like D&D in that there's a party that is facing adversity together. They may bicker, but for most of play they share a the same overall goal.
By contrast, some PbtA games are completely different—the GM is still there to portray the world and to bring life to NPCs, but the players are each other's adversity. There is no party.
These games play out like Game of Thrones, or Battlestar Galactica. Most of the fun comes from watching the interaction between characters that have opposing goals, and none of them is clearly the protagonist.
Example PbtA games that are like this:
- Apocalypse World, where PCs are the various badasses of the wasteland
- Monsterhearts, where each PC is a high school teen-who-is-really-a-monster
- Cartel, which plays out like narco-crime themed telenovelas
Even so, there are many PbtA games that aren't like this, and use the traditional party format:
- Dungeon World (fantasy adventure)
- The Regiment (WWII combat focus)
- Night Witches (all-women Soviet airwomen in WWII)
There are also games that seem to straddle the border, such as Urban Shadows. Here, there's often a powerful adverserial force in the environment, but the PCs have their own problems don't clomp around town like a party.
Genre-Focused Rules
For whatever reason (I suspect mostly historical), a lot of PbtA games have a focus that is nothing to do with combat and scrambling around physical environments, and their resolution procedures reflect this.
For example, because of its focus on supernatural teen drama, the basic resolution procedures in Monsterhearts are for things like:
- Making someone feel dumb or unwanted by shutting them down
- Unexpectedly turning someone on
- Gazing into the abyss for an insight (metaphorically, such as by putting your Depeche Mode mix tape on repeat for the whole night)
- Totally losing your shit and becoming your darkest self
Night Witches has a move to reach out to someone (PC or NPC) and express vulnerability or heartfelt connection.
'Authoring' Rules
Some PbtA do interesting things with traditional GM responsibilities. For example, Urban Shadows is a game of modern supernatural drama—characters might be vampires, werewolves, retired monster hunters, and so on.
Here is the resolution procedure for meeting a new NPC:
When you put a face to a name or vice versa, roll 2D6 + your bonus for their Faction.
- On a 7+, you know their reputation; the GM will tell you what most people know about them.
- On a 10+, you’ve dealt with them before; learn something interesting and useful about them or they owe you a Debt.
- On a miss, you don’t know them or you owe them, the GM will tell you which.
This simple rule has a huge effect on play. Whenever the GM introduces a new NPC, there's a good chance that they will suddenly have meaningful backstory with a PC. The GM can't prepare ahead of time for this, since she has no idea which PC might wind up meeting them first!
This is the sort of rule that you can imagine behind the script when Han introduces the rest of the Falcon crew to Lando in Empire Strikes Back. "Sure, I know a guy.."
I suppose this plays a similar role to B/X D&D's monster reaction table—it keeps the GM on her toes and forces her to try to retroactively figure out why the monster might behave like the table requires, except it operates at the level of backstory rather than immediate visceral reaction.
The Urban Shadows veteran character has a hilarious optional ability:
Catch you fuckers at a bad time? Mark Corruption to arrive in a scene. Mark an additional Corruption to bring someone with you.
Basically, veterans can just kick in the door and show up anywhere with a big bag of guns. From a traditional, players striving against the environment perspective this is downright unusual (isn't it cheating?!), but it's perfect for the genre and has been a lot of fun every time I've seen it used in play.
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For what it's worth, 2G2BT is pretty traditional. It expects that the players are a party, not an ensemble cast, and the rules are mostly focused on combat rather than on the emotional context of the PCs. There is a dash of authoring rules, particularly with the addition of the briefing move, but also in the Urban Shadows-inspired way that PCs recognize NPCs and enemy units.
