There's been a few Masyu variants done with optional Black and White circles. Here's another one, with a extra twist. The twist is taken from the Castle Wall genre. I think the puzzle worked out nicely. The optional quality makes the puzzle a bit trickier. Maybe the next time I'd make the puzzle a bit bigger, to make the twist play out more.
I know I've been making more variants the last few weeks. That's why I've added an extra tag for all puzzle variants and hybrids to find them easier on the blog. I've left the variant tag off the Sudokus as every Sudoku is a Sudoku variant. If people think I should also add it to them, I will.
Rules for Masyu
Follow normal Masyu rules. Additionally, not every black and white circle has to be visited by the loop. If a black circle isn't visited, it will be located outside the loop. If a white circle isn't visited, it will be located inside the loop.