1. Choose an basis which is firm. Cover this with clay. I chose a flattened tin can, without lid or bottom.

2. Begin with the heart of the flower, I chose purple. Use a different colour for the flower petals and cover the ball with them (leave the "front" uncovered). The flower petals are made of clay using real leaves as mould. The petals can overlap each other, but do leave some openings. Put the ball on your basis.
Model a stem of a beautiful green colour.
 

3. Bake the basis with the flower in an ordinary oven for 30 minutes (110 degrees). Let it cool by itself. Meanwhile, start with the hedgehog. Make two balls of tin foil and fasten them together, using a cocktail stick. Cover this form with a not so thin layer of clay. This is its ground form. Give it two feet.
 

4. Form the head. His backside will be a darker shade of clay. My hedgehog is warm so he has a blush. I gave him sunglasses too. To model him a bit easier I put him on the backside of a glass bowl. 
 

5. Make his arms. One of them has been strenthened by a wire. As the arm is only fastened at his shoulder, it could sag while baking it. His quills are made of cocktail sticks, made black with a permanent marker. I only used the ends. Put the hedgehog on the underground and give him some props.

The creation is now ready to be baked (again). Same temperature, same time.

I hope you now have an impression of what is possible using polystyrene foam forms (see also my haunted house).