An Empty monster box is one of the raw materials required to make any kind of monster in the Monstercrafting skill (the second material being Monster fragments). It can be bought from the Homunculus' shop for 10 coins each. When a player uses the other raw materials required with the box they will receive a trapped monster (the type of monster depends on what materials are used with the box) in the box. Doing this will give the player a significant amount of xp. If a player releases the monster then they will receive an extra amount of xp but not as much as creating the monster.