Hold & Win respin

The mechanic

• Each spin can land one or more coin symbols.
• Coins lock in place for the rest of the round.
• Respin until no new coins land for 3 spins — or the grid fills (grand jackpot).
• Bonus twist: 3 coins on the middle row = mini-jackpot.

Setup

1. Register coin symbol

builder.symbols((r) => {
  r.register('coin', BlockSymbol, { colors: { coin: 0xffb74c } });
});
builder.weights({ coin: 3 });

2. Track held positions

const held = new Map<string, string>();   // "r,row" → symbolId

reelSet.events.on('spin:complete', ({ symbols }) => {
  for (let r = 0; r < symbols.length; r++) {
    for (let row = 0; row < symbols[r].length; row++) {
      if (symbols[r][row] === 'coin') held.set(`${r},${row}`, 'coin');
    }
  }
  if (held.size === symbols.length * symbols[0].length) grandJackpot();
});

3. Feed held cells back into the next spin

On every spin, build the target grid yourself — keep held cells as coins, fill the rest with random non-coins. This is exactly what holdAndWinProgress does in the cheats library.

function buildGrid(held, size, coinChance) {
  // 1. empty grid with held cells pre-filled
  // 2. roll a coin for each free cell with `coinChance`
  // 3. fill remaining with random non-coin noise
}

4. Cheat: guaranteed progression

Use holdAndWinProgress('coin', 1) for demos — every spin lands a new coin, so you reach the jackpot in a few clicks instead of playing through RNG.

engine.register({
  id: 'guaranteed',
  label: 'Guaranteed coin each spin',
  enabled: true,
  cheat: holdAndWinProgress('coin', 1),
});

Testing the jackpot

engine.setHeld(heldAlmostAll);   // 8/9 cells on a 3×3 test board
const r = engine.next();
expect(r.meta?.jackpot).toBe(true);