A Sharp 8×8 Puzzle Solved with Forced Chain in 16 Steps

This 8×8 board rates as sharp (difficulty score 945). Solving it from scratch takes 16 logical steps, using 8 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Paired regions, Shape squeeze, Forced chain. Every step below is forced: nothing here is a guess.

1. First, every open cell left in this region sits in column B, so its marker has to land there; that clears every other open cell in the column.
2. Next, every open cell in column A 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.
3. Then, together, two regions have open cells only in rows 4 and 5; 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.
4. After that, 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.
5. Now, every remaining candidate in this region touches D6 and D7, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
6. From there, every open cell left in this region sits in column E, so its marker has to land there; that clears every other open cell in the column.
7. Following that, marking A1 would force E3 (the last open cell in row 3), then D8 (the last open cell in column D), then C6 (the last open cell in region 7), and then column F would be left with no open cell for its marker. So A1 can't be the marker there.
8. First, every open cell in row 1 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
9. Next, place a marker at A2. Row 2 has exactly one open cell left. Placing here clears the rest of row 2, column A, and its region.
10. Then, place a marker at E3. Row 3 has exactly one open cell left. Placing here clears the rest of row 3, column E, and its region. Placing here also clears its 1 touching neighbour.
11. After that, place a marker at D8. Column 4 has exactly one open cell left. Placing here clears the rest of row 8, column D, and its region. Placing here also clears its 1 touching neighbour.
12. Now, 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.
13. From there, 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.
14. Following that, place a marker at G5. Region has exactly one open cell left. Placing here clears the rest of row 5, column G, and its region.
15. First, place a marker at H7. Region has exactly one open cell left. Placing here clears the rest of row 7, column H, and its region.
16. Finally, place a marker at F1. Region has exactly one open cell left.

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