It is only dropped by the two Hollow Black Mages that accompany the Executioner's Chariot in the Undead Purgatory. This staff is one of the three or four best staves in the game (for Int-based sorcerers), but it's extremely rare. So I put myself through the misery of trying to farm the Lizard Staff for my sorcerer character. I hadn't played as a dedicated caster in the original release, so I made the sorcerer my primary character for Scholar. I made myself a knight character as well as a sorcerer character.
I've been trying to get myself hyped up for Dark Souls III by playing through the Scholar of the First Sin edition of Dark Souls II.
