Diablo 4: Vessel of Hatred early leveling guide
Start the Season 6 Season of Hatred quest FIRST. Season 6 quests are marked in BLUE. This kicks off in Zarbzinet and will direct you to fight a Realmwalker. More info later on this but the reward gives you a consumable 'Seething Opals' that have an XP buff and stack with Elixirs and Incense. You can then use these during the campaign.