Originally posted by Capcom:

From Friday, December 14 00:00 a.m. to Thursday, December 27 23:59 UTC,
one of the most dangerous arch-tempered elder dragons arrives on Steam!

- Take on the Event Quest "The Deathly Quiet Curtain" to slay an Arch-tempered Vaal Hazak!
　・Arch-tempered monsters can be distinguished from their normal counterparts by
　 their slight metallic gleam.
　・When taking on this Event Quest, the color of the frame around the monster icon
　 will be different than usual, so keep an eye out!
　・You need to be Hunter Rank (HR) 50 or higher to take on this quest.
　・Please note that the availability of this quest is subject to change without prior notice.

- Craftable equipment:
　・Vaal Hazak γ armor series
　・Death Stench Layered Armor

- Known bugs:
We have confirmed a bug that prevents you from selling items on the rewards screen after completing the Kulve Taroth Siege quest, if the item box contains the maximum number of
that item (9999).
　・This bug prevents you from individually selecting and selling the item in question,
　 　and from jumping from the item icon to the Sell All option with the cursor.
　・This only occurs when you possess the maximum number of an item.

Before going out on the Kulve Taroth Siege quest, please make sure you do not possess (close to) the maximum number of any of the reward items.
We apologize for the inconvenience.