According to the guidebook to Simon's Quest, Dracula's Fang is a relic Simon Belmont never knew about. It was kept in the basement chamber of the castle where Dracula was resurrected in and it became Dracula's Ghost's only weapon against him in that game.
The Tooth of Vlad (which in reality is the Nail in the original Japanese version) is one of the items necessary to enter the Reverse Castle Center. It adds STR +10.
The Fang of Vlad is one of the six relics needed to enter the ceremonial room. It provides a DEF +10 stat boost (a function that had been previously provided by the Rib of Vlad in Symphony of the Night). It can be found in the Clock Tower's boulder race room (Castle A), in the small room to the left. There's no wall to break to gain entry to that room, instead Juste must slide through a hidden crawlspace.
An icon depicting two vampire fangs is located at the left side of the Rib of Vlad.
By opening the internal graphic data of Castlevania II: Simon's Quest, it is possible to locate the icon for what is presumably Dracula's Fang among the other relics. Said relic is not present in the final game and is only mentioned in the storyline.
