What Counts as a Difficult Clear

A precise list, because the back-to-back bonus depends entirely on it.

The game divides clears into difficult and ordinary. The distinction only matters for one thing, the back-to-back bonus, but that bonus is worth enough to make the definition worth knowing exactly.

The list

Difficult clears are:

Any clear of four rows at once.
Any T-spin that clears at least one line.
Any mini T-spin that clears at least one line.

Ordinary clears are everything else: singles, doubles and triples without a spin.

The two edge cases

A T-spin that clears nothing. It scores points, but it neither starts nor breaks a back-to-back chain. It is neutral, and your existing chain survives.

Placing pieces without clearing. Also neutral. You can build for twenty pieces without clearing a line and the chain stays live. Back-to-back is not a timer.

So the only thing that breaks a chain is an ordinary clear.

Why the line is drawn there

The clears classed as difficult are the ones requiring setup. A four-row clear means keeping a well open for many pieces and resisting the urge to fill it. A T-spin means constructing a notch and executing a rotation-last placement.

Both involve declining easier clears in the meantime. The bonus exists to make that patience worth something.

What it means at the table

The badge beside your well tells you whether a chain is live. When it is showing, ask before every clear: is this ordinary? If so, taking it costs you 1.5 times on everything that follows.

That is not always the wrong choice. A stack fourteen rows high needs relief more than it needs a multiplier. But it should be a decision, not a reflex.

In versus

Back-to-back also adds one row to every attack. Over a sustained exchange that extra row per clear is frequently the entire margin, which is why strong versus players will accept a genuinely uncomfortable board rather than break a chain.