Bridges
Ten boards from 5×5 to 7×7 with 3 to 8 threads. Each board has one or two bridges.
On a bridge two threads cross: one runs over it, the other under it, across. No turning on a bridge, and both passes must be filled — one thread going straight across left to right, another top to bottom. It is the only place where threads may cross.
That makes a bridge a strong clue rather than an escape hatch. It fixes four directions at once, so ask early which two threads can use it. The levels grow harder in order; the last few take patience. Read the bridges guide, or play them in Small & mean mixed with other twists.