I had a look at Rubix's Lix level, but I get the feeling that - outside of perhaps...
...a VERY difficult-to-execute solution via the nuke...
...it's going to rely on knowing Lix much better than I do in order to notice the solution.
Video:
https://youtu.be/NgJXUFgxSAg
I also solved both of Colorful Arty's SuperLemmini levels. Both were alright, but nothing special, IMO. Replay is attached for the first level; I forgot to save it for the second one (but the video is there, at least).
Video:
https://youtu.be/Ee4Gv-npGfw
A general tip I'd like to put out there for contest entrants (and just to clarify - this is a piece of advice from me,
not a contest rule in any way!) - the contests probably aren't the best place to show off some obscure and annoying-to-execute trick. Based on past results, nor is it really the place for "how can I make a level as hard as possible". Both of these kind of levels have tended to do quite poorly in past contests; levels that are challenging but not
too hard, not a pain in the ass to perform the solution to, and most of all, fun to play, are the ones that tend to do best. Of course there are exceptions - "Parking Garage" for example was probably the hardest level in the contest it was entered in, and not only did it win that contest, but also came 3rd in Level Of The Year 2015 - but in general, remember that the entire community are the judges, and this includes people who do not like fiddly execution, as well as people who are not great at solving overly difficult levels.