The Seven Pieces, One by One

What each shape is good for, what it ruins, and why S and Z are the ones that end runs.

Seven shapes, because there are exactly seven distinct ways to join four squares edge to edge. Each has a personality worth knowing.

I, the long one

Four in a line, cyan. The only piece that can clear four rows at once, and the only one that reaches the bottom of a deep well. Flat surfaces love it; uneven ones have almost nowhere to put it.

Hold it if your well is not ready. Wasting an I laid flat across the top of a stack is one of the most expensive mistakes available.

O, the square

Two by two, yellow. The only piece that does not rotate. Completely uncomplicated: it needs a flat two-wide space, and it never creates an overhang.

Slightly deceptive because it is so easy to place. An O dropped somewhere merely acceptable raises two columns and gets you nothing.

T, the useful one

Three in a row with one on top, purple. Fits flat surfaces, single-cell notches, and, crucially, can be spun into covered gaps for a T-spin.

If you are learning one advanced technique, it is a T-spin, and this is the piece it needs. Consider holding a T when the setup is close.

L and J, the mirrored pair

Three in a row with one at the end, orange and blue. Useful and forgiving. They fill single-column gaps at the edge of a stack, tuck under overhangs when rotated, and sit flat when you have nothing better.

The workhorses. Most of a clean stack is L and J doing unglamorous work.

S and Z, the difficult pair

Two offset pairs, green and red. These are the pieces that end runs.

An S or Z on a flat surface always leaves a hole underneath unless placed against a matching step. They want a surface with a one-cell height difference in the right direction, and if your stack does not have one, you are choosing between a hole and a spike.

The habit that follows

Because S and Z are guaranteed to arrive, once per bag, every bag, a good stack keeps somewhere for them. A perfectly flat surface is not actually ideal; a surface with a gentle step or two accepts S and Z without damage.

That is the single most useful thing to know about the piece set: build for the awkward pieces, because the easy ones fit anywhere.