This update holds a big part of the game: The levelling mechanics. Another big thing is the new map you can play if you are level 4 or above. From now on will your characters have levels and level up by destroying other mobs of various levels. Gear also has levels which influences their stats. There are also statpoints you can spend from here on to unlock certain features. Furthermore there are lots of bugfixes and there is new music included in the game.
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