Less than ten? Tricky 11 can be done with no builders at all!
Tricky 12 - Bitter Lemming50 Lemmings
Save 80% (40)
Release rate 1
8 minutes
50 climbers, floaters, builders; 20 of all others
Good: Interesting terrain makes for a variety of solutions; uses other skills as well as builders. Turning the release rate up to 99 and making everyone a floater is a fun way to solve it
Bad: The "splat start" is a bit discouraging for first-time players.