Innies/outies of a single row, column, or box. medium killer only
Comparing the tinted rows/columns' 45-total against the cages leaves the marked cells, which must total 18; no assignment reaching it allows 3 in R3C7.
Every row, column, and box sums to 45. Comparing that total against the cages lying fully inside leaves a small set of cells (innies or outies) with a known sum: a virtual cage you can reason about.