Inspired by a Rassi Silai variant by bakpao, I wanted to explore the idea of omitting exactly one cell per region with other genres. Double Back seemed like a particularly good fit, so this is where I tried it first. I also decided to give it a slightly more evocative name. :)
If you use the puzz.link solver, the “Check base type” button should complain about exactly one unvisited cell per region if you have the correct solution.
Rules: Draw a non-intersecting loop through the centres of all empty cells which passes through each region exactly twice.
Variant: Forgetful — The loop omits exactly one cell in each region.