Play Sunstone: The Fifth Sun — a free Aztec block puzzle in your browser

Sunstone: The Fifth Sun is a free browser block puzzle. Fit carved obsidian blocks into the Sunstone altar, clear lines to relight the sky, and finish thirty chapters of Aztec myth to free Princess Citlali.

Sunstone: The Fifth Sun is a free browser-based block placement puzzle built around Aztec myth. You are Yaotl, a young stone-carver of the Calmecac, and the altar in front of you is a grid carved into obsidian. Three carved blocks wait in the tray beneath it. Drag one onto the altar; when every free cell of a row or a column is filled, that line clears, the stone rings, and the flame in the sky grows a little stronger. Complete the chapter's objective and one band of the Sunstone seals shut.

Thirty chapters are split into four bands — Flint, Rain, Jaguar and Death — and each one carries a piece of the story of Princess Citlali, who was taken into the Smoking Mirror because a mirror needs somebody inside it to be a mirror at all. Beyond the campaign there is an endless mode, New Fire Cycles, where the piece pool tightens every twelve placements and the sun sets if you leave eight placements without a completed line.

How to play

1. Pick a block. Drag one of the three carved blocks from the tray onto the altar, or tap it and then tap the socket you want.
2. Complete a line. A row or column clears when every free cell in it is filled. Obsidian idols already on the altar count as filled cells.
3. Stack the fire. Keep completing lines on consecutive placements to raise the streak multiplier up to x5 — score is where two and three star ratings come from.
4. Spend the objective. Some bands ask for a number of lines, some for every dawn glyph on the altar, some for every obsidian idol shattered, and some for a target amount of fire.
5. Watch the tray. If none of the three blocks in the tray fits anywhere, the chapter ends on the spot. Leave a few flat, open cells near the edges and a big piece will always have somewhere to land.
6. Seal the band. Meet the objective before the placement budget runs out and the chapter is sealed: one star for the win, two at the two-star fire line, three at 1.4x that line.

Controls

The four bands of the Sunstone

Goals, idols and glyphs

Idols are a gift and a trap at the same time. They already count as filled cells, so a line through an idol looks half finished when you arrive — but an idol sitting in the middle of a row you need can only be removed by closing the perpendicular line, and every idol you leave on the board is a cell you can never place a block into.

The five carving tools

Block puzzle vs. match-3 vs. mahjong

Why it is hard in a good way

Block placement looks like luck and stops being luck the moment you understand one thing: every placement is a permanent promise about shape. A two-by-two square dropped in the middle of a nearly empty altar is four cells of raw material. The same square dropped at the end of a nearly finished row is the last thing you need. Same piece, opposite value — the difference is entirely about where the flat ground is.

The altar's shape matters just as much. The stepped pyramid in the Rain band has narrow 4-cell rows along its top and bottom, which is free money for a careful carver; the crossroads in the Jaguar band has hollow corners, so any piece that wants to straddle an edge has to be rotated in your head before you let go of it. Blindly dropping pieces into the widest space is the fastest way to jam the tray and lose a chapter with the objective three lines away.

Strategy that actually works

• Keep one corner flat. A 2x2 or 3x3 piece needs a square of flat ground; if you shave every corner, those pieces become dead weight in the tray.
• Commit to a pair of lines early. Filling two adjacent rows at once scores double the line points and keeps the streak multiplier alive for far longer than clearing one line at a time.
• Treat idols as scaffolding. They count as filled cells. A row with two idols in it is a 6-cell row, not an 8-cell row — that is usually the cheapest objective on the board.
• Bank the streak, don't chase it. Every consecutive clearing placement raises the multiplier by 0.5 up to x5. One dry placement resets it to x1, so sometimes the right move is the safe line instead of the flashy one.
• Spend tools to protect the objective, not the score. Rain is worth more when it claims the last glyph in a sign than when it clears a random row for points.
• In New Fire Cycles, count to six. Stay at least two placements away from the eight-placement sunset at all times; an eight-clause rule is a much harder master than an empty altar.

Technical notes

The whole game is a single self-contained web page with no third-party scripts, no trackers and no network calls after load. Rendering is HTML5 canvas 2D at a logical resolution of 720x1040, redrawn at the display refresh rate with a device-pixel-ratio aware backing store, so it stays crisp on retina screens. Art is generated in code: volcanic grain, the rotating Sunstone mandala, carved obsidian blocks with engraved glyphs, gold hairline trim, shatter shards, light beams and the fire aura that brightens as your streak climbs. Audio is synthesised on the fly with the Web Audio API — stone clacks, glyph bells, crack-and-shatter and a low temple drone — so the download stays tiny.

The puzzle engine is deterministic. Each chapter seeds a small pseudo-random generator and draws its piece stream from it, which means the reference carver used to balance the game plays the exact same sequence you do. Every chapter's two-star line and objective target in the game were measured by playing thousands of chapters with that reference carver, not guessed: a chapter only shipped when the bot could win it in at least nine out of ten seeded runs without spending a single tool.

Progress is stored locally in your browser under sunstone.save.v1 — unlocked chapters, star ratings, best scores and sound preference. Nothing is uploaded anywhere. There is no account system, because there is no server.

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