Bas relief projects can range from volcanoes for science projects to plaques.  Since this is a Halloween site, this will lean more towards this theme.  The materials are few, simple, cheap (or free) and easy to work with: a choice of plywood, masonite, foamcore, or corrugated cardboard; old newspapers and masking tape; heavy-duty aluminum foil; a choice of white PVA (Elmer’s) glue, flour and water paste or wallpaper paste; acrylic paints; urethane sealer; assorted brushes and containers and a covered work surface.  You’ll need a baseboard or platform to start.  Plywood or masonite work well, and are very strong.  All you need to do is paint them, and you’re ready to go.  For a lighter weight baseboard, begin with foamcore (used for mounting posters and pictures) or several glued together sheets of corrugated (box) cardboard.  To gain the strength you’ll need, foamcore and cardboard laminates should be covered with at least three layers of strip paper mache.  The inner structure will be created from wads of newspaper secured with painter’s masking tape.  The size and number of wads depends, of course, on the finished size of your project.
To make a simple plaque or raised design, lightly sketch the shape of the base of the design on the baseboard.  Wad up pieces of paper and secured with masking tape in the appropriate location on your project.  The sizes of the paper wads might vary from ping-pong ball size up to grapefruit size.  Tape wads to the baseboard, filling in the sketch.  Now, begin piling up and taping down, wads of paper to form the shape.  You can cover the whole works with heavy-duty aluminum foil to make the surface easier to papier mache.
Cover the aluminum foil with two or three layers of torn-strip paper mache.  When the paper mache is dry, either paint it with acrylic paint, or add another layer of paper mache .  After painting the project, seal it with several coats of clear urethane.
 

The first thing you need to do is collect several good pictures (photographs and or drawings) of alligators and crocodiles - crocodiles are funnier, they have long skinny snouts with a bump on the end.  The next thing to do is create the armature, or basic form.  For this you use big wads of crumpled newspaper and lots of masking tape.  The body is an extremely elongated oval, flat on top.  The head is long, lumpy and bumpy (especially over the eyes and nose) and consists mostly of mouth, with the teeth sticking out.  The legs are stumpy and the feet pudgy.  If you are really ambitious (or just plain nuts), you can make the reptile in one piece but making the parts may be easier to do and less stressful.  Squeeze and pinch the newspaper wads, adding more paper and tape until you get the shapes the way you want them.  The teeth can be cut from cardboard or poster board, or you could form them from little tight wads of paper and tape.  The same process can be done for the toenails.  Tape all the body parts together.  Cut rectangles of various sizes from cardboard, and tape them to the back of the head, body and tail for "armor plating."  Cover the entire armature with multiple layers of torn-strip paper mache.  If you’re going to paint, the final layer of paper mache should be white which provides a good contrast for the colors you paint it.  Seal with multiple coats of clear, gloss urethane.