Forum_account's Pixel Movement library actually includes a Zelda demonstration. Once downloaded, expand the zelda-demo folder and check both demo.dm and map.dmm.

BYOND's native pixel movement isn't really all that different than the tile movement you're used to. If you have a clear understanding of tile movement it shouldn't take much to wrap your head around pixel movement. Density, Bump(), step(), all that stuff pretty much works exactly the same with pixel movement as it does with tile movement.

The first variable you should get accustomed to using is step_size. It's a variable used to determine how many pixels an atom moves per step. The default is 32, basically moving one full tile per step. Lowering it to 16 for example will cause the atom to step 16 pixels rather than 32, a half tile rather than a full tile. Lowering it even further will allow smoother pixel movement, but with the default tick_lag the atoms will move around quite slow. With the fps variable you can set the frames per second, increasing it from 10 to 30 will dramatically increase the speed of your game but keep in mind that will also increase the required processing power of the computer running it.

The variables bound_width and bound_height are used to determine the size of an atom. By default everything is 32x32 (bound_width=32,bound_height=32), that's one full tile. If you wanted an atom to only take up a half tile you would set it to 16x16 (bound_width=16,bound_height=16). If an atom is smaller than a full tile that means it can collide with other small atoms occupying the same tile.

That small bit should be enough to set you in the right direction. You can read more about pixel movement here.