Experience

Experience (very often abbreviated exp or XP) is what allows you to level up. To gain experience you can, for example, kill mobs, of which bosses being what brings the most exp. Every time you level up, you gain 2.5% more attack and bonus of XXX health also a badge next to your name. When you level up, you get bronze stage badge then silver stage badge, gold stage badge, golden star stage badge and finally star badge. After you get a star badge, the process will be repeated with a star badge you got until you get 12 stars. 
If you put on an experience doubler pendant, you will collect twice the experience that you would collect without this pendant.
The 50 players with the highest level in the game are listed in the General Ranking. There is no limit to the levels you can get.
Image credit: Tayaress
==Trivia==
*A badge stage has 4 badges each. Once you level up, you can only get one badge. That means you have to get 20 levels to get a star badge.
*An advanced player is usually with more badges.