blueprint - 1959015 - room to stand

Not a terribly complicated mechanism, but it produces a really cool "shrinking ground" effect:

http://i.imgur.com/CTXal.png

The "Piston Elevators" map I reference is long dead, but you can see a picture of it here.

2072480 - grass skew

The ground skews left/right which makes it hard to climb. Unfortunately, like a lot of maps, sync and lag can alter the timing by a little bit, and mice can get stuck inside the grass (temporarily).

2036283 - eternal walljump

How to make wall jumping more annoying? Make mice jump up the same walls over and over again... There's extra friction on the right side to help with the wall jumping with cheese.