I don't know if this is how NL currently works, but one thing I've learned from constructing levels with optional challenges in DROD is that sometimes you want to hide the challenge until the room has been solved, because merely stating what the challenge is spoils something about the room's solution. In DROD there's an in-game element -- the green door -- that allows challenge scrolls to be placed, but blocked off until the player has solved a room. In NL, the equivalent would be a "hidden" talisman that gets automatically revealed when a level is solved.
That said, because the games are so different, I'm not entirely convinced this is a useful feature for NL. Normally, one expects that all the skills are required for a level solution (unless it's either an N-of-all or a "Proxima-type" level). So if the talisman is, for example, "Solve with 5 or fewer builders", that just says that it's possible (and harder) to solve that way, and doesn't tell you much about the intended "main" solution.
