A Medium 6×6 Puzzle Solved with Shape Squeeze in 15 Steps

This 6×6 board rates as medium (difficulty score 856). Solving it from scratch takes 15 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Shape squeeze. Every step below is forced: nothing here is a guess.

1. First, every remaining candidate in this region touches B2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
2. Next, every remaining candidate in this region touches D5, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
3. Then, every open cell left in this region sits in column C, so its marker has to land there; that clears every other open cell in the column.
4. After that, every open cell left in this region sits in row 1, so its marker has to land there; that clears every other open cell in the row.
5. Now, every open cell left in this region sits in column A, so its marker has to land there; that clears every other open cell in the column.
6. From there, every open cell in column B belongs to the same region, so that region's marker has to be somewhere in this column; that clears every other open cell in the region.
7. Following that, every remaining candidate in this region touches E2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
8. First, every remaining candidate in this region touches B3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
9. Next, every remaining candidate in this region touches C5, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
10. Then, place a marker at C6. Region has exactly one open cell left. Placing here clears the rest of row 6, column C, and its region. Placing here also clears its 1 touching neighbour.
11. After that, place a marker at B4. Region has exactly one open cell left. Placing here clears the rest of row 4, column B, and its region. Placing here also clears its 1 touching neighbour.
12. Now, place a marker at A2. Region has exactly one open cell left. Placing here clears the rest of row 2, column A, and its region.
13. From there, place a marker at E5. Region has exactly one open cell left. Placing here clears the rest of row 5, column E, and its region.
14. Following that, place a marker at F3. Region has exactly one open cell left. Placing here clears the rest of row 3, column F, and its region.
15. Finally, place a marker at D1. Region has exactly one open cell left.

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