If you want to jump into MU Legend's second closed beta but still didn't find a way to do so, then you can follow Webzen's kind advice and play this entire weekend with a special key that works for all players. If you go to the MU Legend website and use the beta key LORENCIA, you're good to go for a couple of days.
This second closed beta officially ends on February 28 and after that the developers will be working on preparing the game for the open beta.