Bernkastel
Reaper of Miracles
Wade tells a joke that appeals to his former human self. While the dragon is amused and distracted Deapool uses his magic satchel to remove a syringe full of AIDS. He injects it into the dragon and walks away. The dragon eventually dies while Wade sits at home watching episodes of Beakmans World.
I figured you'd do some research, but just reading Wikipedia isn't enough. That dragon has scales powerful enough to withstand strikes from magically infused blades So... what exactly is needle going to do?