The new event was implemented with four new demons(Ace Frost, Yoshitsune, Trumpeter and Mother Harlot), new musician weapons which can be upgraded mixing 2 of the same to use almighty skills and alot of new D Souls!
The Instance is at TMG Building, by talking with Jack Frost you will get 3 Quests to complete the three difficult modes. The "plates" are the keys you got on post or you can get more doing DM, talking with him everyday and exchanging SP for them...but really, 14k SP for one key?!
Completing the Instances you get Candles, chance of D Souls, chance of music weapons and very rare chance of the new plugins.
You can exchange Candles for many things at Pyro Jack inside TMG Building. The items you can get includes the Music Weapons and PG of the new Demons...but getting around 36 Candles per day wont let you get anything good, lets just hope they increases the Candles or something.
*I updated Demon Fusions and New Demons sections with the new info.
And here videos of the three instances i made, enjoy!
Official Page:
http://www.megatenonline.com/7th_anniversary/event.html