Doubling

Doubling is a calm number-merging puzzle played with clay pebbles on a wooden tray. Every swipe slides all the pebbles at once in one direction. When two pebbles with the same number meet, they press together into one pebble worth double, and a new small pebble drops onto the tray. A 2 and a 2 make a 4, two 4s make an 8, and so on.

The campaign has 120 trays across eight worlds, each with a clear goal and a move budget. Some trays ask you to make a pebble of a certain value, some to peel away every clay slab, some to thaw every frozen pebble, and later ones ask for a score. Every fifth tray is a challenge and every fifteenth is a boss tray with several goals and a tight budget. Stars depend on how few moves you use, and every tray was played through by a bot to set a fair budget.

Each world adds one idea to plan around. The Pebble Garden brings rocks that never move and oddly shaped trays. In the Clay Beds, some cells sit on stacked slabs, and every merge that lands there peels one off. In the Frost Pond, frozen pebbles cannot move until merges next to them crack the ice, and thick ice needs two hits. Mud Flats add sticky mud that holds any pebble sliding into it, the Star Kiln adds star pebbles that merge with anything and double it, and the last two worlds mix everything on bigger boards.

A few tips go a long way. Keep your biggest pebble in a corner and build toward it, so it does not drift into the middle and block merges. Use rocks as walls: pebbles stop against them, which lets you line up pairs. On slab and ice trays, plan merges that land on the right cells rather than just making big numbers. You get one free undo per tray, and the mallet can smash a single pebble if the tray fills up, so save it for a real emergency.

Coins from cleared trays buy pebble finishes such as river marble, candy and carved wood, and tray woods like oak, walnut and birch. When you just want to slide without goals, classic endless mode on a 4 by 4 tray keeps your best score. Each tray is a small, self-contained puzzle, which suits quick sessions, and the game plays with swipes, a mouse or the arrow keys on phones, tablets and computers in any orientation.

On each tray you try to reach the goal before your move budget runs out. Think about where the pebbles will go before you swipe, because every move shifts the whole tray. Coins from cleared trays buy new pebble glazes and tray woods.

When you just want to slide, classic endless mode is there, and it keeps your best score. If you get stuck, the mallet smashes a single pebble, and on a keyboard Z undoes your move.