>>543782523
>Let me Solo Him: The Underpin: Defeat The Underpin in his lair on Tier ?? without any other players in your party, before the release of the next season of Delves. (Reward: Mount Customization: Delver’s Gob-Trotter Schematic: Gold.) Becomes a low drop chance with The Underpin kill after the end of the season.))
>Becomes a low drop chance with The Underpin kill after the end of the season.))

https://worldofwarcraft.blizzard.com/en-gb/news/24223772/updated-81-last-chance-for-the-war-within-season-2-achievements-and-rewards