Last Remaining Cell
Last Remaining Cell flips the question: instead of asking which digit a cell can hold, you ask which cell a digit can go into. Pick a digit, look at a house where it's still missing, and rule out every empty cell that's blocked by that digit sitting elsewhere. If only one cell is left unblocked, the digit goes there.
What is Last Remaining Cell?
Pick a digit from 1 to 9 and find a house where it's still missing. For each empty cell in that house, check whether the digit already appears in the row, column, or box that cell belongs to. If it does, that cell is blocked. When every cell except one is blocked, the one that's left has to take the digit. Not a guess — the grid leaves no other option.
Finding the cell
Start by scanning the board for a digit that's already been placed a lot — something like a 2 or 5 that shows up in several boxes. For each house where it's still missing, mentally block off the rows, columns, and boxes that already contain it. Whatever cell is left at the intersection is your candidate. This pairs naturally with Last Free Cell: placing a digit in one house often creates a Last Remaining Cell in a neighbor. Solvers use it to crack open sections that look stuck.
Combine with scanning
Last Remaining Cell rarely gets used on its own. Most solvers alternate between hunting Last Free Cells and Last Remaining Cells in a single pass over the board. As the puzzle fills in and more digits land, the technique gets easier — fewer cells are left ambiguous. Combined with notes, pairs, and singles, it carries a lot of the work at medium and hard difficulties. The more you do it, the faster you recognize the visual pattern of a digit locked into one spot, which is what makes expert puzzles tractable.