The Dagger Fang appeared as an award in the "Level-Restricted Challenge No. 28" Online Event, given to the Top 10 players (Top 20 if in co-cop). It re-appeared in the "Weekend Survivor No. 21" Online Event for players who beat all 30 missions.
Bibliography
Tada, Takuji, ed (2015). BIOHAZARD REVELATIONS 2 ULTIMANIA. Square Enix.