Fights under your rules

Under a rule system, fights use the system's own numbers, on the same battle map, with the same painted effects and the same turn as everywhere else. A system runs its fights one of two ways. Engine

The system names three things, all formulas:

The attack check

A fight-only check the storyteller never picks outside a fight. Classic d20: d20 + ability modifier + proficiency against the defence, a natural 20 a critical, a natural 1 a miss.

Damage

What the player's hit deals: 1d8 + max(@str.mod, @dex.mod). Twice the dice on a critical.

Defence

What enemies must beat to hit the player: 10 + @dex.mod (an unarmoured Armour Class), or Hope and Fear's Evasion.

Enemies roll the same check, using their template's attack number as their stat. Each blow's roll gets a chip like any other: d20 (14) + 3 Strength + 2 = 19 vs 13 · Hit.

In a consequences fight the player rolls their action, and the outcome is read both ways. The storyteller's words set the stakes: position says how hard a failure hits back, effect how much a success achieves. Engine

Harm becomes health. On a player, each level of harm costs a share of their maximum health (Forged: a quarter, a half, four-fifths, all of it). An enemy is taken out by its template's number of harm levels: a minion by one or two, a boss by six or more.

Any system can add who goes when, and how much a fighter can do in a turn. Engine

1. 1Initiative, onceWhen the first exchange starts, every fighter rolls the system's initiative check once (Classic d20: d20 + Dexterity modifier). Highest first; a tie goes to the player. A fighter who joins later rolls when they first show up.
2. 2A faster foe strikes firstAn enemy ahead of the player in the order lands the blow it announced before the player's action. Cutting it down this turn won't stop that blow.
3. 3Down firstIf a faster foe's blow drops the player, their action never happens.
4. 4The action budgetThe player has the system's actions for a turn: Classic d20 gives an Action (two attacks from level 5) and a Bonus action. Attacks past that are stamped NO TIME and don't happen.

The turn order shows above the battle map as a strip, with each fighter's initiative. Party fights use the same order: blows land in initiative order within the round. See Playing together.

"turn": {
  "initiative": { "check": "initiative" },
  "actions": [
    { "id": "action", "name": "Action", "per": "1", "attacks": "if @level >= 5 then 2 else 1",
      "description": "The main thing they do: an attack (two from level 5), a spell, a dash, a dodge" },
    { "id": "bonus", "name": "Bonus action", "per": "1",
      "description": "A quick extra on top: an off-hand strike after attacking, a quick spell" }
  ] }

An ability can give more actions this turn: Classic d20's Action Surge is an effect, “one more Action this turn”, so a fighter who surges really gets the second Action's attacks rolled.

Everything that tips an attack roll is read before the dice, never added to the result after it. The roll's chip says what tipped it (“Tipped by: Flanked: advantage · Prone (close by): advantage”). Engine

A foe's blow has a type when nothing gives it one: its creature's own, else what the attack's words name (claws are slashing, a bite piercing, flame fire), else the system's default. Someone who can't act (Paralyzed, Stunned, Asleep) makes no blows and uses no abilities, a potion included.

{ "id": "prone", "edge": "-1", "checks": ["attack"],
  "against": [{ "edge": "1", "reach": "near" }, { "edge": "-1", "reach": "far" }] }
{ "id": "paralyzed", "noActions": true,
  "against": [{ "edge": "1" }, { "crit": true, "reach": "near" }] }

A condition put on with a save each turn (Hold Person, a ghoul's claws) lets its bearer roll again at the end of each of their turns, against the DC worked out when it landed; a pass ends it. Foes' conditions count down each exchange, the same as a hero's.

A reaction happens outside the hero's turn, one a round. Nobody stops the round to ask: each hero sets standing orders on their sheet, and code uses the reaction when its moment comes, with a chip. Engine

Any ability can be a reaction: it uses the system's reaction (combat.reaction) and says when it fires (react.on: hit, spell, or leave) and what it does. Reactions are never picked as the turn's action. A blink (Misty Step) and the system's disengage words never provoke an opportunity attack.

{ "id": "shield", "kind": "Spell", "level": 1, "cost": [{ "slot": 1 }],
  "uses": "reaction", "react": { "on": "hit", "defence": "5" } }

An ability can be held (sustained): Hold Person, Bless, and the SRD's other concentration spells. What it puts on carries who holds it. It ends, and what it put on comes off everyone, when: Engine

• they use another held ability (one at a time);
• they are hurt and fail the system's combat.sustain check (Classic d20: a Constitution save against the higher of 10 and half the damage), rolled on every blow that hurts them;
• they drop.

The sheet and the storyteller both see what they hold.

Every enemy the storyteller brings into a system world gets a sheet from the system's templates. Its role (minion, standard, elite, boss) comes from what it is in the scene; its tier, 1 to 6, from how dangerous the world says it is. Templates are formulas of the tier: Engine

{ "role": "standard",
  "defaults": { "attribute": "min(5, floor((@tier + 1) / 2))" },
  "tracks":   { "hp": "8 + 6 * @tier" },
  "combat":   { "defence": "12 + @tier", "attack": "@tier", "damage": "(@tier)d6 + @tier" } }

Change a template in the Advanced tab, or ask Hob (“make bosses tougher at tier 3 and up”). Enemies already in the world keep the sheet they were given.

A character's ability aimed at foes takes over their first blow of the turn: an attack spell rolls its own attack and dice; a save spell rolls its harm once and each foe's save against the caster's DC. A creature from the bestiary fights with its own numbers, attacks a turn and abilities: a breath weapon is a save the player rolls. Damage types meet what a creature resists or fears, and regeneration closes its wounds unless what stops it struck. See Spells and abilities and The bestiary. Engine

Fights set off cards like everything else: a fight starting or ending, each blow's damage dealt or taken, each foe defeated.

A condition can say what it means for a hero at 0 hit points: dead or stable. Code reads it with the world's own death rules. In a world with death, a hero marked Dead dies there; in a world without it, or once Stable, they stop bleeding out and come to later.

Who wins a fight, and how the storyteller tells it, works as it does without a rule system: see Fighting. Storyteller