How to solve this 9×9 logic puzzle

9×9 · steady · 15 steps

This 9×9 board rates as steady (difficulty score 795). Solving it from scratch takes 26 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Paired regions, Shape squeeze. Every step below is forced — nothing here is a guess.

First, every open cell left in this region sits in row 1, so its marker has to land there — clearing every other open cell in the row.
Next, every open cell in column 9 belongs to the same region, so that region's marker has to be somewhere in this column — clearing every other open cell in the region.
Then, together, two regions have open cells only in rows 8 and 9 — with one marker each, those two markers have to fill exactly those two rows, so every other region's open cells there can be cleared.
After that, place a marker at row 7, column 5. Region has exactly one open cell left. Placing here clears the rest of row 7, column 5, and its region. Placing here also clears its 3 touching neighbours.
Now, place a marker at row 6, column 2. Region has exactly one open cell left. Placing here clears the rest of row 6, column 2, and its region. Placing here also clears its 2 touching neighbours.
From there, place a marker at row 8, column 1. Row 8 has exactly one open cell left. Placing here clears the rest of row 8, column 1, and its region.
Following that, place a marker at row 1, column 8. Column 8 has exactly one open cell left. Placing here clears the rest of row 1, column 8, and its region. Placing here also clears its 2 touching neighbours.
First, place a marker at row 9, column 7. Column 7 has exactly one open cell left. Placing here clears the rest of row 9, column 7, and its region.
Next, every open cell left in this region sits in column 6, so its marker has to land there — clearing every other open cell in the column.
Then, every open cell left in this region sits in column 4, so its marker has to land there — clearing every other open cell in the column.
After that, every remaining candidate in this region touches row 2, column 3 and row 3, column 3 — so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
Now, place a marker at row 4, column 3. Region has exactly one open cell left. Placing here clears the rest of row 4, column 3, and its region. Placing here also clears its 1 touching neighbour.
From there, place a marker at row 2, column 4. Region has exactly one open cell left.
Following that, place a marker at row 5, column 6. Region has exactly one open cell left. Placing here clears the rest of row 5, column 6, and its region.
Finally, place a marker at row 3, column 9. Region has exactly one open cell left.

The key move here was Shape squeeze — once you can spot that, this board falls quickly. ∎