Each Witcher game introduces several minigames to divert from the main gameplay. The Witcher 3‘s addition is Gwent: a deck-building card game that is structured to resemble warfare. In the context of the game’s world, there has just been a long war that engulfed the nations that your character calls home, and the cards in the game reflect the factions and characters involved in the war. (Not germane to the use of the system herein, but it does a really good job of reminding you of characters you’ll be encountering in the main plot: if you’ve seen their cards in the game, you know who they fought for and what their general role was.)

A good overview of the game can be found here. But for the highlights:

  • Each player must have a deck of at least 22 cards, and ten are pulled for the match.
  • Each card has a value associated with it.
  • You alternate turns playing cards. Either player can pass instead of taking a turn (but then the other player gets as many turns as desired until she also decides to pass).
  • The goal is to have the highest score at the end of a round (after both players pass), and win two rounds out of three.
  • You don’t normally draw more cards during a match, so the basic strategy involves tricking the other player into using up all of her good cards for an easy first win, leaving you with enough cards to win two rounds. Or just having a much more powerful deck with more high-value cards than the other player (cards are collected during play of the larger RPG, rather than any kind of balance being involved in forming the decks at the time of a match).

When you first start playing, the highlights are all you really need, but as you gain more cards and face opponents with better decks, you start to notice deeper functions:

  • Cards are siege, ranged, or melee. Different special effects modify cards based on what type they are.
  • Many cards have special abilities such as being spies (lets you give the card to your opponent’s tally, but draw more cards from your deck), medics (lets you instantly play a card from your discard pile), morale boosters (increases every ally card of the same type by +1), mustering (lets you play every card with the same name instantly even from your main deck), tight bonders (doubles the point value of identical ally cards), or agile (lets you treat the card as ranged or melee when you play it, whichever works better for your strategy and available cards).
  • Special cards can be weather effects that reduce all cards of a certain type to base value 1 (for both players), warhorns that let you double all ally cards of a particular type, scorch cards that take out all the cards with the currently highest value (possibly including your own if you aren’t careful), and decoys that let you pull a card back into your hand (to take back a high-value card after forcing your opponent to waste cards to counter it, or to pick up a spy that your opponent has just used so you can turnabout and turn it into a triple agent, drawing more cards yourself).
  • The most notable characters in the game are hero cards. Heroes are generally very high value, and are immune to negative effects (they can’t be reduced by weather or scorched). Unfortunately, they’re also immune to positive effects (they can’t benefit from warhorns or morale boosts, be restored by medics, or be picked back up with a decoy).
  • Each faction has a special ability and can have one version of a commander card (with an additional once-per-match special ability).

Taken together, what initially seems like a slightly more complicated version of War actually proves to have tremendous strategic and tactical depth.

And it might be a really good system for doing mass combat for D&D/Pathfinder.

In particular, things it does by default that work well for d20 include:

  • There’s a built in understanding that one protagonist is worth a whole unit of basic NPCs: cards with a named character are generally worth more points than cards that represent whole units. This tends to jibe with actual D&D play in a way that most mass combat systems don’t: clearly, a single PC with good defenses and AoEs is able to mow unharmed through a whole squad of lower level soldiers.
  • The heroes system seems purpose-built to represent PCs and major NPCs.
  • The point value of cards maps pretty directly to level, while special abilities can represent specific training boosts.
  • It’s much faster and more fun to play than traditional mass combat systems.

Specific changes I’d make to the game to fit it specifically into a campaign include:

  • Decide early on how many soldiers are needed to create a unit card. This can be many or few, as the drawing system will wind up balancing them. Larger creatures might need fewer for a unit (e.g., a unit of archers might represent 40 characters, but a unit of Ogres only 10). Also decide whether non-hero NPCs are just the face of a unit (e.g., is that NPC card just representing him, or him and a support staff?). This will influence how much you need to force the PCs to care about paying for their units during downtime, and should ultimately reflect how many mooks you think a single PC could take out during a battle.
  • Figure out what the bar is for gaining a special ability. The standard game features cards that don’t have specials and ones that do, and if you’re using level as the card’s value number it’s harder to balance the card by reducing that level when you add a special. Instead, having a special ability should usually be the sign of an elite unit (possibly one that has better gear, PC class levels, or just some expensive form of training).
  • Figure out whether there are certain bonuses and penalties for setting up a battle. For example, having a stronger battlefield position may let you start the game by drawing more cards than your opponent, or, assuming neither side has a caster with Control Weather, weather cards might be completely up to the GM to play based on the conditions during the battle.

I’d suggest using the normal single-match method of play only for minor sorties with nothing really on the line. For campaign-deciding wars, I’d suggest a version that’s iterated:

  • Each match represents approximately a day of fighting.
  • Each deck represents all available units. If units are moving from distant places to join the war, cards that were not available on day one can be added to your deck for subsequent matches once they arrive as reinforcements.
  • The first match is played normally.
  • At the end of the first match, the loser removes all non-hero cards from his discard pile (they were killed or otherwise totally disbanded), and sets aside the hero cards (they were injured enough that they won’t help in subsequent matches). The winner shuffles her discarded hero cards back into the main deck, and moves the remaining discards to an “infirmary pile” (they’re not dead, and can be pulled from by Medic cards, but will otherwise not be available until the end of the war. Cards remaining in hand (because you passed and won or lost with cards remaining) are shuffled back into the deck.
  • Subsequent matches use the same deck (with modifications for reinforcements and non-injured heroes). If you have multiple players that are interested in having a go, you can trade out which player is in the hot seat from match to match. (On a round that a player is in control, you might consider having her pull her PC from the deck as an automatic add, if not already injured, because playing your own character card is fun.)
  • The war ends when one side gets totally run out of cards or forfeits completely.
  • In addition to deciding who won the war, the end of the game should provide a tally of units that are dead/disbanded, just injured, or still in fighting shape for later wars or just for the general story purpose of describing what happened. You might also consider giving surviving units a chance to level up based on how well everything went.

Ultimately, this should wind up playing similarly to my previously posted card-based battle system (which was fun, but time-consuming to set up), but likely with more feeling of fun and agency for the players (since there are a number of more interesting tactics you can pursue beyond just trying to assemble the biggest army).