Gearing your character up is crucial as you take on stronger monsters, which is why you should refer to a Diablo 4 boss loot table. Each lair boss drops powerful Unique items for your character that transform your skills and help you slay your way through the endgame. Below you'll find the complete list of items for each lair boss in Season 14: Season of Death Awakening.
All of these bosses have a higher chance of dropping one of the ultra-powerful uber Uniques, or Mythic Uniques, than anything else in the game.
Also note that, while the boss Belial doesn't have a specific loot table, you can choose any other boss loot table when you defeat him and you'll get a guaranteed ancestral Unique with one or more greater affixes.
