Here is one innocent-looking 5 by 5 Masyu puzzle:
Inflate it to twice its original size, though, and it turns into a full-blown 10 by 10 Semi-Liar Masyu:
Here is a pair of Masyu puzzles.
Here is a pair of Every Cell Masyu puzzles.
These puzzles were inspired by a Masyu construction challenge posed by Chris Green (Valvino) on his previous puzzle blog, Logic Puzzles. See here for the original announcement and here for the results. Valvino’s current blog is Puzzle Parade.
Both the original challenge and this variant are made very difficult by the fact that – because of the asymmetry in Masyu rules – the black circles are much more restrictive than the white ones.
One way to remedy this is to alter the rules so that the loop only has to go straight either immediately before or immediately after a black circle, but not necessarily both. I call this variant Symmetric Masyu.
So, here is a pair of Every Cell Symmetric Masyu puzzles on a 10 by 10 grid in which both puzzles are fairly interesting to solve: