What kind of game is Tunnel Digger?
You drive a small drilling robot in a hard hat through a grid of underground earth and collect every gem on the board. Moles and ghosts roam the tunnels, and boulders are buried all over the board: dig out the cell beneath a boulder and it drops, flattening whatever is below. The rules come from the classic arcade digging games, with every picture and sound drawn and synthesized in code.
The board is 12 cells wide and 14 cells deep, with sky, clouds and flowers above ground. The earth comes in four layers by depth, topsoil, ochre, red clay and bedrock, and the deeper you go the slower you dig. Wherever the robot passes a tunnel remains, and the monsters follow those tunnels to chase you. Collect all the gems to advance a stage; touch a monster or get caught under a boulder and you lose a life. You start with three lives and gain one for every five stages cleared.
When does a boulder fall, and when does it shatter?
The moment the cell directly below a boulder is emptied, the boulder wobbles for 0.7 seconds and then falls. Any monster in its path is crushed for big points, and the robot is crushed too if it stays in the way. A boulder that drops only one cell settles in its new spot; one that drops two or more cells shatters when it lands.
| Situation | What the boulder does |
|---|---|
| Earth below it | Stays put |
| Cell below fully dug out | Wobbles for 0.7 seconds, then falls. Get out of the way while it wobbles |
| Cell below still being dug | Still counts as earth. It only wobbles once the cell is finished |
| Falls one cell | Becomes a resting boulder again. Dig under it to drop it once more |
| Falls two or more cells | Shatters and disappears on landing |
| Monster in its path | Crushed for 500 points. A second monster under the same boulder gives 1,000, a third 2,000 |
| Robot in its path | The robot is crushed and you lose a life |
Boulders are cells the robot cannot dig through, so they also act as walls. Go around one and dig beneath it and it drops into the tunnel below, changing the shape of the board, which makes boulders a tool for reshaping your escape routes.
How do the two monsters differ?
Moles move only through tunnels, while ghosts can turn translucent and fly straight through the earth toward you. Both start asleep in small pockets underground and wake up after 1.5 seconds.
| Monster | Movement | Watch out |
|---|---|---|
| Mole | Chases the robot along the shortest tunnel route. If its pocket is not connected to your tunnels it paces inside | Left trapped for long enough it starts digging toward you on its own. Tunnels dug by moles can drop boulders too |
| Ghost | Follows tunnels, but when it has no path or you are close it turns translucent and flies through the earth | It is slow while flying, but walls mean nothing to it. Once it enters a tunnel it goes back to following tunnels |
Stage 1 has two moles. The count grows with each stage up to eight monsters, ghosts appear from stage 2, and every monster gets a little faster each stage.
How is the score calculated?
Gems are worth 20, 50 or 100 points by type, and crushing monsters with a boulder starts at 500 and doubles for each extra monster under the same boulder. Clearing a stage pays a bonus of 100 times the stage number, plus 50 if you still have your firework.
| Item | Points |
|---|---|
| Emerald (green) | 20. Common near the surface |
| Ruby (red) | 50. Common at medium depth |
| Gold (yellow) | 100. Common deep down |
| Monster crushed by a boulder | 500, then 1,000 and 2,000 for the second and third under the same boulder |
| Monster blown away by the firework | 200 each |
| Stage clear | Stage number × 100, plus 50 if the firework is unused |
What changes as the stages go up?
More gems, more and faster monsters, and more boulders. Stage 1 starts with 9 gems and two moles; stage 20 packs 16 gems, eight monsters and eight boulders onto one board.
- Gems: 8 plus the stage number, up to 16. Deeper layers hold more gold.
- Monsters: about 0.6 more per stage, up to eight. Trapped moles also start digging sooner.
- Boulders: 4 to start, one more every three stages, up to 8.
- Lives: one extra when you enter stages 6, 11 and 16.
- The end: clear stage 20 and the result screen shows that every stage is done.
When is the best time to use the firework?
You get one firework per stage, so the best moment is when two or more monsters close in and there is no tunnel left to run down. Every monster within two and a half cells of the robot is blown away for 200 points each.
Finishing a stage with the firework unused pays 50 extra points, but a life is worth far more than that. When a ghost has flown through the earth to your side, or moles are closing from both ends of a tunnel, spend it without hesitation. The firework has no effect on boulders.
Any tips for a high score?
- Prepare tunnels under boulders ahead of time. If a boulder sits over the route a monster will take, dig out the cell beneath it just as the monster passes underneath. Leaving exactly one cell under a boulder and waiting beside it is the basic trap.
- Do not connect everything into one long tunnel. Once tunnels run everywhere, moles can reach you from any side. Dig short branches to the gems and double back, and the moles stay stuck in their pockets for a while.
- The moment the cell under a boulder is finished, step sideways. The 0.7 second wobble is all the time you get. Keep digging straight down and the boulder lands on your back.
- Deep gold pays best, but bedrock is the slowest layer to dig and the hardest place to flee. Dig an escape tunnel before you start mining it.
- Keep moving when a ghost turns translucent. It flies toward where you are now, so sprinting along a long horizontal tunnel is the easiest way out.
- The surface is a tunnel too. Monsters come up to the surface, so it is no place to rest. Instead dig several entrances from the surface so you always have another way down.
Controls
- Keyboard: arrow keys or WASD move in four directions. Moving into earth digs through it; moving into a tunnel runs fast. X or Space sets off the firework, and on the title and result screens Space or Enter starts a game.
- Phone and tablet: push the round joystick at the bottom left to move, and tap the yellow button at the bottom right for the firework. Pressing and dragging on the board also steers.
- Mouse: press and drag to move in that direction; a short click sets off the firework.
- Top right buttons: sound on or off and back to the menu. The sound setting is kept in this browser.
All graphics and sounds are drawn and synthesized in code, so nothing is downloaded. Your best score is kept only in this browser and never sent to a server.