Here's a small challenge for Taxing 9 (Perseverance). I might've had mentioned some form of it on the old old forums, but hopefully it remains unknown to most:
Solve the level with 3 skills (out of the ones given to you in the level), such that no lemmings ever go horizontally beyond the right edge of the starting platform (as in, past the rightmost column of pixels of the starting platform, applying this boundary even when you get down to the lower platform of the exit). From the level editor, this translates to no lemmings' x-position ever going above 812.
Too easy? Find two different ways to do it. (Obviously any differences that do not affect the solution in any meaningful way doesn't count. I can tell you that the two ways I know of involve different skills used.)