Open Program The first step in any creating anything in Maya is to start up the Program and set you project folders.
Create Project Folders To create your project folders, once Maya has finished loading, go to the file menu and go find the find where it says 'Project.' Highlight 'Project and another menu should pop out. In that menu select 'New.'
Set Project Folder WIndow Once the 'New Project' Window opens as shown, define the name of your project in the 'Name' box and where you'd like everything related to your project to be saved in the 'Location' box. You may also use the 'Browse' button to browse to the desired location. To simply the creation of all necessary sub folders, simply hit the use 'Use Defaults' button at the bottom. When you're sure everything is the way you want it, hit 'Accept.'
Check Reference Now before we get carried away, it's best to check a reference image first. Such an image can be found using a Google image search. For our purposes were going to use this easily recognizable character. For what we're trying to do, you're going to want to find an image that makes it easy to determine how many pixels made up the sprite. In the case of the Goomba here, he's 17 across by 16 vertical for a total of 272. Bear in mind that's not how many pixels in the image, that's how many pixels the original sprite occupied on screen including white space.
Create Cube Now that we've determined the the number of pixels that made up the original sprite, we can begin recreating it using cubes in 3D. The first thing we'll need to do is create a cube. Each cube is going to represent a pixel. Once back in Maya go to the 'Create' menu and select 'Cube' and click on the square next to option for Cube to get the creation options. I don't have a picture, but at the side of your Maya screen you should get some Cube creation options, namely it'll give you the option to define the desired length, width, and height. I recommend leaving it a 1x1x1.
Cube Created Once you're satisfied with the dimensions of your cube, click anywhere on the grid and Maya will create it for you.
Duplicate Cube The next step is to duplicate that cube. You remember that the Goomba was 17 pixels across? That means we're going to need 17 cubes. So to duplicate your cube you'll need to select it by clicking on it ensuring that it turns green and then going to the 'Edit' menu and selecting 'Duplicate.' Now you're initial duplicate is going to appear in the same spot as your initial cube so you're going to want to select the 'Move' tool, it's the one with the picture of cone with an arrow under it. Move you're duplicate cube off to side a bit by click on the red arrow. For each subsequent duplicate, go back to the 'Edit' menu and select 'Duplicate with Transform' and your new cube should appear to the side of the original. Repeat until you have 17 cubes.
Join Duplicates Next you'll want to move all you're cubes as close together as possible. Ideally you'll want the left and right edges to be in virtually the same position, or as close as you can get. The easiest was to do this is to switch to the top view by hitting the Space Bar key then when the four views come up mouse over the top view and hit the Space Bar again.
Dropdown Menu At this point you're going to want to make sure you're menus are set to 'Polygons' in the upper left hand corner you should see a little drop down menu like the one shown here. If it doesn't currently read "Polygons" click on it and change it to 'Polygons.'
Combine cubes Now that we're sure we're looking at the right menus, you'll want to select all the cubes and combine them into one object. Click off anything you may have currently selected and then click anywhere on the grid and drag out a selection box to highlight all your cubes. Once they're all selected, go to the 'Mesh' menu and select 'Combine'. This should combine them all into one object.
Merge Verticies Even though all your cubes are now considered one object, you still have to merge all the vertices together. Right click anywhere on your object and change to 'Vertex' mode.
Merge Vertices pt. 2 Click and drag to highlight the vertices where the individual cubes join together.
Merge Verticies Pt 3 Once the vertices are selected, go to the 'Edit Mesh' menu and select 'Merge.' Repeat this process for every set of vertices where the individual cubes join together.
Duplicate Row Now that we have an entire row done, we need to duplicate it. Return to Object Mode, the same way you did Vertex mode by right clicking and selecting it or by simply click anywhere off the object. Once back in object mode, re-select your row, if you deselected it, and just like we did for the individual cubes, go to the 'Edit' menu and select 'Duplicate.'
Duplicate + Transform As before, your duplicate will appear in the same spot as the original, so select the Move tool if it's not already selected and move your duplicate so that it sits above your original row. Now if you remember again back to the reference image, the Goomba was 17x16 pixels, that means we need 14 more rows, so go back to the 'Edit' menu and like before select 'Duplicate with Transform' so that the duplicate will appear above the original. Repeat until you have 16 rows.
Combine Rows Now, again much like before, we need to combine these, but before we can do that we need to move them so that their top and bottom edges are as close to being in the same position as possible. Again this can be best accomplished by changing to the Front view by hitting Space Bar and mousing over the desired view and then hitting Space Bar again.
Combining Rows Pt 2 Once you've got all the top and bottom edges as close together as you can get them, then like before, click and drag to select all the rows and go to the 'Mesh' menu and select 'Combine' to combine them all into one object
Merge Vertices Once again, like before, you're going to need to merge the vertices where the individual rows join. Like before, right click anywhere on your object and sect the Vertex mode.
Merge Verticies Again Once in Vertex mode you're going to need too click and drag to select all the vertices where the rows join. That includes the ones on the interior too, so yes each individual cube, but don't worry, only the top and bottom vertices Don't forget to do both sides.
Select Faces Once all the vertices are merged, it's time to start removing the white space. Change to 'Face' mode in the same manner you changed to 'Vertex' mode (right click on object and select desired mode). Now you can begin removing the white space. Because all the faces of each individual cube still exist, don't forget to remove them all where appropriate.
Extra Faces Now you may have noticed that some of your edges look kind of shiny. That's because you've got two faces in the same position. You'd think that merging vertices would also mean merge associated faces as well, but with Maya apparently it doesn't. So with any of these just go ahead and remove the extra faces.
Apply Colour Now we're ready to apply some colour. Because our sprite is rather detailed, we're going to want to remain in Faces mode. First you'll want to select all the faces you want to apply your first colour to, or you could just select one. In any case, right click on the desired face(s) and that same mode switching menu should pop up, but you'll notice and additional menu underneath it. In that menu go down to where it says 'Assign New Material.' I recommend going with the Lambert for simplicity's sake and also if you're doing 8-bit sprites, 8-bit sprites didn't have the most vibrant colours.
New Material You should notice that a your new material's attributes have appeared on the right hand side of your screen as pictured here. You can modify these attributes as you see fit. To give your material a name, click in the box under where it says "Lambert:" (or whatever material you chose). To change the colour click on the box next to where it says 'Color' and a Colour Chooser should pop up.
Colour Chooser The Colour Chooser should look something like this. To define your desired colour you can click on the swatches, play with the sliders, or click anywhere on the colour cube. Alternatively you can input the RGB values of the colour you want directly if you know them. However you'll probably want to change the range. Maya, by default, has the RGB range set to go from 0 to 1 so you'll want to use the drop down menu I've highlighted to change that to 0 to 255. Once you've done that you can input the RGB values directly into the highlighted fields.
Assigning Existing Material Once you've created the material once, you don't have to create it again. To assign your created material to another face, select that face then right click and find where it says 'Assign Existing Material.' Find your Material in the menu that pops out and click on it to assign it to the selected face. Don't forget to colour both the front and back as well as the left, right, top, and bottom of your sprite. It is 3D after all.
Finished Product If you've coloured it properly (or however you desired to colour it) referring back to your reference image when need be, it should come out looking something like this.