The Vault Keeper is the main boss in Season 3 of Diablo 4, but that doesn’t mean the Son of Malphas can’t show up to protect his demon dad. If you want an extra battle with some decent loot, I’ll go over where you can find the optional boss in the Season of the Construct.
Where to Find the Son of Malphas in Diablo 4
The Son of Malphas can appear as a random boss encounter in one of the five Nightmare Vaults on World Tier 3 or higher. Nightmare Vaults can only be accessed after reaching World Tier 3 and they serve as the upgraded version of Vaults from the main quest line in Season of the Construct. Any time you enter one of the higher-level Vaults, the offspring demon can appear.
