This event was introduced last week. I haven't attempt it yet since it's troublesome to take note of the time. It seems like some rewards are fairly good, even though they are not listed in the event page. This has led to a drop in prices for premium characters and rings.
Basically, raid a specific mission within 1 hour of the listed time. If you get a specific item determined by GM at the start of the event for that day, you will get a reward (also specified by GM in server notice) after the event ended.
Also, no maintenance today, so Christmas Event will be extended for a week.
Okay, I tried doing the one for Demonic Minotauros. It was rather bad. I was getting lag to the effect of 0.5-2 FPS at the mission gate. The GM wasn't on to announce what item was needed and what the reward would be. If they can't be on at the time, then they should have simply listed the required items and rewards in the event webpage instead.
Gabriela's Retaliation Feb 03-22, 2016
Valentine In New Era Feb 01-20, 2016