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Undead (Simon Tatham's Puzzles)
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About the puzzle
Undead is a grid in which some squares hold diagonal mirrors and every other square hides a monster: a ghost, a vampire or a zombie. Along the edge of the grid are numbers saying how many monsters you can see when you look into the grid from that point, following your line of sight as it bounces off the mirrors. The catch is that the monsters do not all show up the same way. Vampires have no reflection, ghosts can only be seen in a mirror, and zombies are visible either way.
The puzzle was invented by David Millar as the Haunted Mirror Maze. Steffen Bauer contributed this version to the collection in 2012.
Rules
- Every square without a mirror holds exactly one monster: a ghost, a vampire or a zombie.
- The totals at the top say how many of each kind are in the grid.
- A number on the edge counts the monsters visible along the line of sight that starts there and reflects off the mirrors until it leaves the grid.
- Before the line of sight has hit a mirror, you see vampires and zombies but not ghosts. After it has been reflected at least once, you see ghosts and zombies but not vampires.
- Mirrors reflect on both sides. If a line of sight passes the same monster twice, it counts every time it is seen.
Controls
| Input | Action |
|---|---|
| Left click a square, then G / V / Z (or 1 / 2 / 3) | place a ghost, vampire or zombie |
| Left click a square, then a monster in the counts at the top | place that monster |
| Left click a square, then Space | clear it |
| Right click a square, then a letter | add or remove a pencil mark |
| M | fill every empty square with all three pencil marks |
| Arrow keys | move the cursor; Enter switches it to pencil marks |
| Left click an edge number | grey it out as done |
| A | switch between monster pictures and letters |
| C (or right click the counts) | show totals, monsters still to place, or placed out of total |
| N / U / R | new game / undo / redo |
The counts at the top turn grey when you have placed the right number of that monster. In Preferences you can make the letters and the counts style permanent.
How to solve it
Read the zeros. A 0 is the strongest clue. Every square its line of sight crosses before the first mirror must be a ghost, and every square after a mirror must be a vampire. Zombies are ruled out all along it.
Lines without mirrors are simple counts. A line of sight that crosses the grid without touching a mirror sees vampires and zombies, so its number is exactly how many squares on it are not ghosts.
Compare the two ends. A path that bends has a number at each end. The squares between the mirrors are seen in reflection from both ends, so they count the same for both numbers. Only the stretch before the first mirror on each side differs, which makes the difference between the two numbers a clue about the ghosts and vampires at the two ends.
Count squares visited twice. A path that bounces back across itself can see the same monster twice. Squares like that weigh more in the count and are often decided first.
Use the totals at the end. When a few squares are left, the counts of each monster at the top usually settle them. Pencil marks help here: press M to fill every square with all three options, then remove the ones each clue rules out.
Sizes and difficulty
The Type menu has 4x4 and 5x5 grids at Easy, Normal and Tricky, and 7x7 grids at Easy and Normal. Custom sets any width and height and the difficulty.
Playing here
Click Play to open the puzzle. The menu above the board has New game, Restart, Undo, Redo and Solve (which you can undo to keep going on your own), the Type menu with the sizes, and the Game menu, where you can type in a game ID or a random seed, download the current game as a file, load a saved file and change the preferences. Your game in progress is kept in this browser and comes back with its whole undo history the next time you open the page.
On a touch screen, tap a square and then tap a monster in the counts at the top to place it there; tapping the same monster again clears the square. For pencil marks, turn on the Mark button above the board, tap the square, turn Mark off again and tap the monsters you want to note.
Credits and licence
Undead was written by Steffen Bauer for Simon Tatham's Portable Puzzle Collection, which Simon Tatham maintains with code contributed by several other authors and distributes with its source code under the MIT licence. This page runs a WebAssembly build made by FredyGames from the author's official source snapshot, with no changes to the puzzle; the source and the build script are hosted with the game, and the licence text is linked from this page.