Funzzle's expert Sudoku starts with 24 to 28 numbers and needs the advanced patterns: almost every grid has at least one XY-Wing, some an X-Wing or Swordfish. Each grid still has exactly one solution reachable by logic, and the coach can walk you through any step. A new expert grid comes out every day.
Three cells with two candidates each: a pivot XY that sees one cell XZ and another YZ. Whichever digit the pivot takes, one of the two wings becomes Z, so any cell that sees both wings can't be Z. Funzzle's expert grids almost always need one.
If a digit can only go in the same two columns in two different rows, it must take one of those columns in each row, so you can remove it from every other cell of those two columns. Swordfish is the same idea with three rows and three columns.
Not on Funzzle. Every grid has a single solution and our solver reaches it with the techniques listed here, without trial and error.
On Saturday. This page has an expert grid every day.