You can still play this one, there's just no tournament cutoff date or prizes any more. There are three other ongoing arenas here: http://codecombat.com/play/ladder

We're working on the next tournament level, which will be ready for playtesting soon–message me if you want to help! Otherwise, it should be launched in a few weeks, so follow our blog to know when it starts. Not sure whether there will be prizes, but there will be glory.