#Magic Vault 5×3 — Game Design Document

draft-v0.1 — DEV ONLY. NOT FOR PRODUCTION. NOT FOR CERTIFICATION.

#1. Document control

Every RTP or frequency figure in this document is a math result, not a player-facing promise, and none of them is a session guarantee.

#2. High concept

A fantasy vault of heroes, gems and prize coins. The base game is a deliberately plain 5×3 / 10-line slot; almost all of the game's value sits in a Hold & Win that fires roughly once in eighty paid rounds. The player's attention is meant to be on coins landing, not on line wins.

Intended volatility: high / feature-heavy.

#3. Game summary

#4. Symbols

There is no BONUS symbol. COIN appears on the base reels and is the only trigger source. symbol_bonus.png is not used in Draft v0.1.

#Wild rules

• WILD substitutes for H1–H4 and L1–L4.
• WILD does not substitute for COIN, and no arrangement of wilds makes a COIN line pay.
• WILD does not itself trigger, block or alter the Hold & Win.

#5. Paylines

Row indexes are 0 = top, 1 = middle, 2 = bottom. Positions[i] is the row on reel i.

#6. Paytable

Values are line-bet multipliers. The engine divides each line win by the number of paylines, so a 10-line round staking 1.00 total pays payout / 10 per winning line. Feature awards are total-bet multipliers and are not divided.

#Why WILD has no 3- or 4-of-a-kind row

This is a deliberate, tested consequence of the engine, recorded rather than worked around.

mathengine's LinesEvaluator takes the first non-wild symbol on the line as the match symbol. Leading wilds therefore always fold into the run behind them: WILD, WILD, WILD, H2, L1 pays H2 four of a kind, not WILD three of a kind. WILD is the match symbol only when every position on the line is wild — which is exactly five. Publishing WILD 3- and 4-of-a-kind rows would advertise combinations no grid can produce.

Pinned by TestWildThreeAndFourAreStructurallyUnreachable. Changing this would require a change to the shared evaluator, which is outside this game's scope.

#7. Base-game rules

1. Each reel makes one weighted draw and shows a three-symbol window (see the Math Spec §4).
2. Each of the 10 paylines is evaluated left to right from reel 1.
3. A line pays its longest run of matching symbols, with WILD substituting.
4. A line pays at most once; the 10 line results are summed.
5. COIN never contributes a line win. A COIN on reel 1 ends that payline's run.
6. Visible COIN symbols are counted across the whole 5×3 grid.
7. If 6 or more COIN are visible, the Hold & Win begins.
8. The round total is capped once at 500× total bet.

#8. Hold & Win

Mechanic hold_and_win/v1, reused unchanged. The only adaptation is the layout.

#Trigger and carry-over

• 6 or more visible COIN anywhere on the 5×3 grid.
• Those exact cells become the initial locked cells in their own positions.
• The feature never redraws, relocates or replaces a triggering coin.
• Each initially locked cell is immediately assigned exactly one prize.

Cell index is column * 3 + row, columns left to right, rows top to bottom. Cell 0 is the top of reel 1; cell 14 is the bottom of reel 5.

#Respin loop

respins := 3
repeat:
    for each EMPTY cell, in cell-index order:
        with probability 4.3% (43,000 PPM) the cell locks and receives one prize
    if at least one cell locked this step:  respins := 3        (reset)
    else:                                   respins := respins - 1
until respins == 0 or all 15 cells are locked

Locked cells are never redrawn and consume no randomness. The feature charges no additional wager. Background art switches to bonus-background.png.

#Prizes

Each locked cell receives one prize drawn as kind first, then value if the kind is regular.

E[regular] = 3.49×, E[prize] ≈ 3.815789×.

#Settlement

• Ordinary: the sum of all locked prizes, capped once at 500× total bet.
• Full grid: exactly Grand = 500× total bet, which replaces the prize sum rather than adding to it. A grid worth 1,400× in coins still pays 500×; a grid worth 15× still pays 500×.
• There is no landed "Grand" prize kind. The Grand exists only as the full-grid award.

#9. Maximum win

500× total bet, and it is reachable rather than merely advertised: a full grid settles at exactly 500×. Witnessed deterministically at seed magic-vault-golden, round index 62574, and by direct settlement of a constructed full grid at three different per-cell values.

The base game alone can reach at most 64× across all ten lines, so the round cap can only ever bind on a feature round.

#10. Player-facing figures

These are long-run mathematical properties of the model. They are not a promise about any session, and none of them has been externally certified.

#11. Not in Draft v0.1

Free spins, feature buy, Mystery, Scatter, collectors, additional multipliers, additional wagers, gamble, any change to hold_and_win/v1, new art, live routing, deployment, frontend E2E, Final / Freeze / Handoff.