Diablo II
To increase a characters level in Diablo II, the player must run the character around killing the monsters that appear in the different areas.  Once a monster is defeated, it sometimes drops items or coins. When a monster is killed, it will not come back until the game is saved and started again.  Each character has a certain amount of experience that they needs to gain before they can become the next level.  This number depends upon what level the character is.  The higher the level, the more experience is needed to level.