Wings
How it works
Two cells, not seeing each other, that both carry only the same two candidates X and Y. Somewhere else on the grid, find a pair of cells for X that only leaves room for X in one or the other โ a strong link โ with one end seeing the first cell and the other end seeing the second. Whichever candidate the first cell turns out to be, the argument still lands on Y being used up in one of the two starting cells, so any cell that sees both of them can't be Y.
Try it
No worked example for this one yet. It turns up rarely enough that no puzzle has needed it as its next step so far โ one will appear here as soon as a generated puzzle offers it.