These little guys spawn at night and throw nearby blocks at the player. When building, use the picture for reference and attach the arm pieces in this order: Green at the bottom, then magenta, red, then yellow at the top. If you want you can cut holes in the top of the arms and print blocks for him to hold.

Link to mod: http://www.minecraftforum.net/topic/81771-172-mo-creatures-v620-with-ents-and-moles/