Building for the Pieces You Do Not Want

S and Z arrive once per bag, guaranteed. A stack with nowhere for them is a stack that is about to fail.

The seven-bag guarantees you will receive an S and a Z in every group of seven pieces. There is no avoiding them, no waiting them out, and no version of the game where they do not arrive.

So the question is not what to do when they show up. It is what your stack looks like when they do.

Why they are difficult

Both are two pairs of cells offset by one. Laid flat on a level surface, one end sits a cell higher than the ground beneath it, leaving a gap. That is a hole, immediately, with no way to avoid it.

They only sit cleanly on a surface that already has a one-cell step in the right direction. S wants a step one way; Z wants the mirror.

The design implication

A perfectly flat stack is not the ideal surface. It handles I, O, L, J and T beautifully and punishes you twice per bag.

What you actually want is a surface that is mostly flat with one or two gentle steps, ideally in both orientations so either piece has a home.

Maintaining the steps

The steps survive line clears, because clearing removes whole rows and the relative heights stay the same. So once you have a good surface shape, it tends to persist: you are maintaining it rather than rebuilding it every clear.

The threat is drift. A step that grows to two cells is no longer a step, it is a canyon, and only an I or a vertical L or J fills it.

When you have no step

Occasionally an S or Z arrives and there is genuinely nowhere. The options are:

Hold it, if the slot is free and the next piece can create a step.

Stack it vertically against the wall, which raises two columns by two but creates no hole.

Accept a hole in the least damaging column, near the edge and shallow.

In that order. The vertical placement against a wall is underused and is frequently the right answer.

The habit

Every few pieces, glance at your surface and ask whether an S and a Z both have a home. If not, the next few placements should create one.

Read next

• Keep the Stack Flat: The One Habit That Matters MostA flat surface accepts every piece. A jagged one accepts a few. Most runs end because the board stopped accepting what the bag offered.
• Never Bury a HoleA covered gap costs you every row above it. Taking a worse placement to avoid one is nearly always correct.
• Downstacking: How to Dig Yourself OutClearing your way down to a buried hole is a distinct skill, and it is the one that turns bad runs into recovered ones.
• The Nine-Column Stack and the Open WellFill nine columns flat, leave one open, and wait for the long piece. The standard shape for a high score.
• The CPU Opponent and Its Three DifficultiesHow the computer player decides where to put things, and what actually changes between rookie and nightmare.
• Seeded Randomness: Why Both Players Get the Same PiecesA small deterministic generator, one shared number, and two identical bags on different machines.