Brief summary: (credit to Loriri (Idi0ticGenius) for translating)
Dual Option System
Introduced for the following gear:
Tier 11
Omen (aka Veldeg, Guile 2.0, or simply Mid-Tier)
Ambush
Behemoth
Tier 12
Cataclysm (aka VM9)
Leviathan (aka VM9.5)
Dungeons
Harrowhold re-opened as a 20-man raid
Not available for Instance Matching System
There are total of 4 phases and each clears provide different rewards
Drops: Royal Dragon, Superior Innerwear, Goddess Tear, Dyad Niveot Structure, VM9.5 retool items, and Evil Dragon’s Crimson Essence (Leviathan Essence for VM9.5), etc
High-Tier Dungeon Rotation
'Demokron Factory Hard Mode' and 'Timescape Normal Mode' closed
'Bathysmal Rise Hard Mode' and 'Akeron's Inferno Hard Mode' re-opened
Both drops: Accessories (T2), Ambush/VM9 designs materials, Tier 11 Feedstock, Extensive/Premium Alkahests, Materials for Diadem, etc
Velik’s Temple Normal and Hard Mode nerfed, greatly decreased monster HP
GvG
Fixed an issue where a guild can declare and withdraw repeatedly so that the opposing side could not Forfeit
Reduced time required to Forfeit from 60 minutes -> 30 minutes
Increased GvG re-declaration from 1 hour -> 3 hours
GvG declaration cooldown will apply after withdrawal instead of when GvG was declared
Changed GvG declaration fee:
Small - 300 to 500
Medium - 900 to 1200
Large - 1500 to 2000
Changed GvG maintenance fee:
Small - 5 to 15
Medium - 15 to 30
Large - 25 to 45
Items
Changes to in-game method to obtain Dragon Mount
Old method:
scale -(50:1)-> Hardened Egg -(RNG)-> dragon or claw/talon -(8:1)-> Mysterious Egg -(RNG)-> dragon or claw/talon
Becomes
scale -(10:1)-> Old Scroll -(RNG)-> dragon or scroll piece -(40:1)-> guaranteed dragon.
Either method requires 400 scales in total anyways, but you get 5x more attempt on the first RNG method to get dragon (underlined) because you are converting 10 scales per scroll instead of 50 scales per hardened egg.