The rule sounds simple — nothing on top, one side open — and then a tile you expected to be free turns out to be blocked. The edge cases are all about partial overlaps.
Condition one: nothing on top
A tile is covered if any part of any higher tile overlaps any part of it. Tiles on upper layers are offset by half a tile in many layouts, so a single upper tile can cover two lower ones, and a lower tile can be covered by two different upper tiles.
This is why removing one upper tile sometimes frees nothing: its neighbour is still overlapping the tile beneath.
Condition two: one long side open
Left and right only. A tile with tiles above and below it in the grid — its short sides — is still free, as long as nothing is on top and one of left or right is clear.
The blocking tile must be on the same layer and must overlap vertically. A tile half a row offset still blocks if any part of it is beside the tile in question.
Why the rule exists
It is the physical rule from the tabletop version. With real tiles stacked on a table, you can only slide a tile out sideways, and only if nothing is resting on it. The digital version preserves that constraint exactly, which is why the shapes feel like real stacks rather than arbitrary grids.
Reading the turtle
The standard turtle has five layers. The bottom layer is a wide slab of 87 tiles; above it sit 36, then 16, then 4, then a single tile at the peak.
That structure has two consequences. The central stack is deep, so tiles there stay blocked for a long time. And the outer edges of the bottom layer are always free on one side, so those tiles are permanently available.
| Layer | Tiles | Notes |
|---|---|---|
| 1 (bottom) | 87 | Outer edges always free; centre blocked for most of the game |
| 2 | 36 | Blocks the centre of layer 1 |
| 3 | 16 | Clears quickly once layer 4 is gone |
| 4 | 4 | Only blocked by the peak tile |
| 5 (peak) | 1 | Free from the start |
The three protruding tiles
The turtle has one tile sticking out on the left and two on the right, at the middle row. They are on the bottom layer with nothing beside them on one side, so they are free permanently, from the first move to the last.
Treat them as banked moves. Whenever you are down to one or two options, those tiles may be what saves the board — provided you did not spend them in the first thirty seconds.
The dimming is doing the work
Blocked tiles are drawn darker and desaturated. Rather than reasoning about the rule, scan for bright tiles — those are your legal moves.
Common confusions
- 'It looks like nothing is on it.' Check the half-offset tiles above; a corner overlap still counts.
- 'Only one tile is beside it.' One side blocked is fine. Both sides blocked is not.
- 'It is at the edge of the board.' The board edge counts as open, so edge tiles are free unless covered.