An Expert 6×6 Puzzle Solved with Forced Chain in 19 Steps

This 6×6 board rates as expert (difficulty score 1192). Solving it from scratch takes 19 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, 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 F, so its marker has to land there; that clears every other open cell in the column.
2. Next, every remaining candidate in this region touches E1 and E2, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
3. Then, marking A1 would force F2 (the last open cell in region 3), then B3 cleared (every open cell left in this region sits in row 3, so its marker has to land there), then C4 and D4 cleared (every remaining candidate in this region touches C4 and D4), and the chain continues, and then row 5 would be left with no open cell for its marker. So A1 can't be the marker there.
4. After that, that one can't be the marker: at C1 it would force F2 (the last open cell in region 3), then D3 (the last open cell in region 2), then E5 (the last open cell in region 5), and region 6 would be left with no open cell for its marker.
5. Now, marking D1 would force F2 (the last open cell in region 3), then A3 (the last open cell in region 1), then E6 cleared (every open cell left in this region sits in row 6, so its marker has to land there), and the chain continues, and then row 5 would be left with no open cell for its marker. So D1 can't be the marker there.
6. From there, that one can't be the marker: at A2 it would force F1 (the last open cell in region 3), then E3 cleared (every open cell left in this region sits in row 3, so its marker has to land there), then C4 and D4 cleared (every remaining candidate in this region touches C4 and D4), and the chain continues, and row 5 would be left with no open cell for its marker.
7. Following that, marking B2 would force F1 (the last open cell in region 3), then D3 (the last open cell in region 2), then E5 (the last open cell in region 5), and then region 6 would be left with no open cell for its marker. So B2 can't be the marker there.
8. First, that one can't be the marker: at F1 it would force A3 (the last open cell in region 1), then D6 and E6 cleared (every open cell left in this region sits in row 6, so its marker has to land there), then E5 cleared (every open cell left in this region sits in row 5, so its marker has to land there), and the chain continues, and row 5 would be left with no open cell for its marker.
9. Next, place a marker at F2. Region has exactly one open cell left. Placing here clears the rest of row 2, column F, and its region. Placing here also clears its 1 touching neighbour.
10. Then, place a marker at B1. Row 1 has exactly one open cell left. Placing here clears the rest of row 1, column B, and its region.
11. After that, 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.
12. Now, every remaining candidate in this region touches C4 and D4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
13. 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.
14. Following that, 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.
15. First, if D3 were the marker, it would force E5 (the last open cell in region 5), and column C would end up with no open cell for its marker, which can't happen. So it can't go there.
16. Next, place a marker at C3. Region has exactly one open cell left. Placing here clears the rest of row 3, column C, and its region.
17. Then, place a marker at D6. Region has exactly one open cell left. Placing here clears the rest of row 6, column D, and its region. Placing here also clears its 1 touching neighbour.
18. After that, place a marker at E4. Region has exactly one open cell left. Placing here clears the rest of row 4, column E, and its region.
19. Finally, place a marker at A5. Region has exactly one open cell left.

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