Remote Pairs
super-tough
The following puzzle illustrates a Remote Pair, which is a kind of disconnected naked pair, in which a forcing chain connects two squares.
If r2c6=1, then r2c8=2, r3c7=1, and r4c7=2.
If r2c6=2, then r2c8=1, r3c7=2, and r4c7=1.
Thus r2c6 and r4c7 form a naked pair, which I’ve circled above, and any cell which shares containers with both of them, such as r4c6, can have both 1 and 2 eliminated, as shown here.
Eliminating those numbers will solve the 1 in column 6, as only one square remains with 1 as a possibility.