Expert keys
Expert is twenty rooms with three keys. The coral gate stays shut until the dead ends are cleared. Standing on the exit early does nothing.
Diamonds sit in stubs when the maze has enough of them. Clear a stub when you pass it — walking back across twenty rooms for one missed key eats the clock.
Scoring
A ranked finish needs every key, the open exit, and no Hint or Peek. Smaller key boards live on the keys page if twenty feels long. Solve desk can show the cheapest key order on a board you generate there — separate from Marks.
Compared with Hard
Hard is sixteen under fog. Expert is twenty with diamonds and full light. Both are long walks; pick fog for memory, keys for coverage.