[KMS] The First Battle with the Black Mage (Orchid & Lotus)

In GMS. But in KMS he wasn't released until after Angelic Buster and was beatable from the get go. As soon as two Angelic Busters spent enough money and joined together with a Bishop and some binders, that is.

Of course... I was only trying to think of which boss you may have been thinking of though... I can't really think of any beyond that though...