Vampires will be the next threat in Diablo 4: They're coming in the second season, which Blizzard has dubbed the "Season of Blood."
Starting on October 17 in Diablo 4's Seasonal Realm, you'll create a new character and gain "vampiric powers" to battle against swarms of vampires. Each of the classes seem to have new modifications to their skills in the Gamescom Opening Night Live trailer. If it's like Season 1, you'll loot powerful season-specific items that augment your abilities.
As part of the seasonal questline, you'll aid a vampire hunter, named Erys, as she tries to locate a vampire lord. She's voiced by Gemma Chan (Eternals), and will introduce you to the season's twist on Diablo's typical demon slaying.
The Season of Blood will include some pretty huge quality-of-life updates to make restarting as a level 1 character each season much easier:
The ability to farm bosses for specific Unique and Uber Unique items
Paragon Points, Skill Points, Potion Charges, and Obol capacity from earning renown will carry over from the Eternal and Seasonal Realms
Gems won't take up inventory space anymore
Search bar and filter options for your stash
5 new and "returning" bosses
In addition to these changes, Blizzard is reworking how elemental resistances work as well as offensive stats, including Vulnerable, Overpower, and Critical Strike Damage. Endgame Diablo 4 players have discussed a number of problems with how stats like these can limit the number of viable builds in the action RPG's hardest dungeons. Certain status effects, like Vulnerable, provide such a substantial increase in your damage that they overshadow everything else.
Season 2's structure is almost exactly a copy of Season 1: You have a questline with a new character, a new signature boss to fight, and build-altering items. I'm excited to see what outrageously broken builds the vampiric powers will cause when season 2 drops on October 17.