MU is populated by a large variety of monsters, from simple ones like goblins and golems, to more challenging ones such as the Gorgon, Kundun or Selupan.

Players can unlock two classes if they reach a certain level with one character: Magic Gladiator and Dark Lord.

Casting a spell costs MP (mana, or magic points) and sometimes AG or stamina.

Mu Online has a built-in chat system that allows all visible players to communicate easily via text.

Users can add custom players to their Friends List in order to make it easy to keep in contact with one another.