In minecraft is there a way to make any other animals or creatures that you can't just spawn?

Iron Golem - place 4 blocks of Iron in a T-shape, standing upright. Place a Pumpkin / Jack-O-Lantern on the top of the T
Snow Golem - Stack 2 blocks of snow and place a Pumpkin / Jack-O-Lantern on the top
Wither - place 4 blocks of soul sand in a T-shape, standing upright. Then place 3 skeleton heads on top of the three upper blocks

Depends on the creature

for example wither you need soul sand and wther heads

for other creatures you can download mods