Switch blocks swap black and white bits when you hit them. White are pass-through and black are solid, so now you can create gates and stuff. I might add another type that swaps with red.

I originally had it so that when other players hit the switch it would also affect your game, but I decided it was too confusing (a player somewhere else in the level could be messing you up, and it would sometimes get out of sync).

When you enter a level or die, the switches and bits reset back to their original state.