A Sharp 6×6 Puzzle Solved with Forced Chain in 12 Steps

This 6×6 board rates as sharp (difficulty score 969). Solving it from scratch takes 12 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Paired regions, Shape squeeze, Forced chain. Every step below is forced: nothing here is a guess.

1. First, together, two regions have open cells only in rows 1 and 2; 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.
2. Next, place a marker at E3. Region has exactly one open cell left. Placing here clears the rest of row 3, column E, and its region. Placing here also clears its 3 touching neighbours.
3. Then, 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.
4. After that, 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.
5. Now, together, two regions have open cells only in columns A and B; with one marker each, those two markers have to fill exactly those two columns, so every other region's open cells there can be cleared.
6. From there, marking A1 would force C2 (the last open cell in region 2), and then row 4 would be left with no open cell for its marker. So A1 can't be the marker there.
7. Following that, if B1 were the marker, row 2 would end up with no open cell for its marker, which can't happen. So it can't go there.
8. First, 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.
9. Next, place a marker at C4. Row 4 has exactly one open cell left. Placing here clears the rest of row 4, column C, and its region. Placing here also clears its 1 touching neighbour.
10. Then, place a marker at B6. Region has exactly one open cell left. Placing here clears the rest of row 6, column B, and its region.
11. After that, place a marker at F5. Region has exactly one open cell left. Placing here clears the rest of row 5, column F, and its region.
12. Finally, place a marker at D1. Region has exactly one open cell left.

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