All monsters are in and working now:
Goblin. Moves 45px (=1 square) towards king.
Eye monster. Moves 80px towards king.
Ghost. Teleports to random location, or move 60px towards king.
Mammoth spider. Moves 60px in random direction, or 60px towards king.
Giant slug. Moves 45px towards king. Creates two smaller slugs when destroyed.
Dragon. Moves 45px left or right or up or down, then shoots a fireball.
Time to make levels and menus.