A digit every cage sum requires, confined to one unit, leaves the rest of it. medium killer only
Every combination of the cage requires 2, and all its homes share one unit. Erase it from the unit outside the cage: R8C7, R9C7, R9C8, R9C9.
When every valid combination of a cage contains a digit, and all of that digit's possible positions in the cage share a row, column, or box, the digit is claimed. Erase it from the rest of that unit.