I've made a test level for everyone to use and gained some information:
1.) Shimmiers can reach 19 pixels high. If a ceiling is 20 pixels above them they cannot reach it anymore. (Bottom left chamber)
2.) Shimmiers can handle 1 pixel of height difference every new horizontal pixel. So if there is a 2 pixel heigh step they will fall. (Top left chamber)
3.) A climber can be given a Shimmier a few frames before he hits his head. Instead of falling down he will turn into a shimmier in the opposite diection. The skill gets taken from the panel when the climber transtions. (Bottom left chamber)
4.) Shimmiers can't go outside the ceiling of a level. The terrain ends there --> they fall down. (Top left chamber)
5.) Shimmiers can't go outside the left/right edges of a level. The terrain again ends there --> they fall down. They land at the very edge of the level if they can land. Giving the player 1 frame to turn them around. (Bottom right chamber)
6.) Shimmiers will stop if the ground gets too close to their feet. I don't have the exact threshold here as in clear physics mode I think you can't currently see the exact position pixel of the shimmier. Can you give the exact ammount here, Nepster?
(Bottom left chamber)
7.) Shimmiers can use the checkerboard mechanic to go up. So inverted to walking where lemmings can't go up. (Bottom left chamber)
8.) Shimmiers can't use the checkerboard mechanic to go down. Again, inverted to walking where lemmings can go down. (Bottom left chamber)
I think 7.) and 8.) are choosen right by Nepster as Lemmings "walk" upside down with their hands here, but I think this will be the most controversial points out of these.
Test level atttached, you'll need L2_Sports! Happy discussing.