Use the [arrow] keys to navigate your man of mystery along the levels; use [space] to jump. After a couple of warmup levels, you'll need to master the art of Shift. You'll never guess what button you have to press...
Shifting flips you beneath the floor on which you are standing, and reverses both your body color and gravity. Thus, if you were at the bottom of a black pit, shifting will put you atop a white mountain, from where you might have more freedom to move. It's up to you to spot the paths that are available using this mechanism, and to figure out how to make it to the exit for each level. Hindering — or occasionally helping — your progress are impassable platforms, which can be rotated out of the way by collecting the proper key.
Short but sweet, Shift shouldn't sap your surplus seconds. The best legitimate scores clock in at just over 4 minutes. However, those minimal minutes are made magnificent not just with the clever mechanic, but through its noir mystique and the little bits of funny sprinkled throughout. At times you'll feel at the mercy of the borderline sadistic but ultimately merciful god-author Tony, but you get a sweet trophy at the end, so it's definitely worth the little shenanigans he throws at you.
That's not to say Shift doesn't have its problems. There are a couple of glitches that can happen when you're near either an edge or a moving door, and there's at least one level where it's possible to get stuck without the luxury of being able to hit restart or throw yourself onto some nearby spikes. Nonetheless, these are very forgivable flaws when viewed in light of the whole.