Skyscraper

Skyscraper is a degenerate (and easier-to-spot) cousin of X-Wing. Two rows each have a digit confined to exactly two cells. One column is shared between the two rows — that's the 'base.' The other two cells stand in different columns — those are the 'roof.'

Because one of the roof cells must be the digit, anything that 'sees' both roof cells (shares a row, column, or box with each) can't be the digit.

Skyscraper hits a lot of cells that X-Wing would miss, and it fires more often.

When to look for it

Run through each digit, listing rows that have exactly two candidates. Whenever two such rows share a column, you have a skyscraper.

How to apply it

1. Pick a digit.
2. Find two rows (or two columns) where it has exactly two candidates each.
3. Identify a shared column (or row) — the 'base.'
4. The other two cells are the 'roof.' Eliminate the digit from cells seen by both roofs.

Example