Undercell: Logic Puzzle
A pentomino logic puzzle. Five-cell pieces lie hidden on the board and the arrows around them point the way. Every board has one solution and can be solved without guessing.
Free. No ads, no accounts, no in-app purchases, no data collected.
How it works
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Read the sensors
A sensor's arrows point toward the nearest cells belonging to a piece. Pieces never touch, even at a corner.
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Mark what you prove
Add Piece and Empty notes as you reason. A hint names one forced cell and explains the step that forces it.
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Lock the piece
Lock a cell or a connected marked group. If every locked cell belongs to a piece, they open together. Locking one empty cell ends the board.
In the game
What's in it
- Twelve difficulties: 6×6, 8×8, and 10×10 boards in easy, medium, hard, and extra-hard.
- Larger locks earn more points, and a harder difficulty pays more for the same lock.
- Up to three stars per board, based on how many hints you take. Successful locks build a persistent rank.
- When the hint counter runs out you can keep taking hints. That board then earns no stars or points.
- Save boards and share challenge codes without sharing your progress or the solution.
- Built-in tutorial, light and dark themes, sound, haptics, full keyboard controls, and screen reader support.
- Works offline, in the browser and on Android.