Rule: Act-End bosses aren't usually supposed to drop, although you can get them to drop on occasion.
Act I
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Blood Raven (Cold Plains)
Griswold (Tristram)
~Sometimes~ Andariel (Catacombs Lv. 4)
Act II
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~Sometimes~ Radament ([aka King Leoric] Sewers Lv. 2)
~Sometimes~ Duriel (Tal Rasha's Tomb)
Act III
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Witch Doctor Endugu (Flayer Dungeon Lv. 3)
Stormtree (Lower Kurast Entrance)
Battlemaid Sarina ([Ruined Temple] Kurast Bazaar)
Icehawk Riftwing ([Sewers Lv. 2 Entrance] Kurast Bazaar)
~Sometimes~ Mephisto (Durance of Hate Lv. 3)
Act IV
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~Sometimes~ Izual (Plains of Despair)
~Sometimes~ Diablo (The Chaos Sanctuary)
Act V
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Snapchip Shatter ([Icy Cellar] Ancient's Way)
Baal (Worldstone Chamber)
Super Unique Monsters:
Classic.battle.net
