The aswang whip is a special whip created by Filipino villagers to drive off aswangs that hunted their villages.
According to legend, to keep the aswang away, Filipino villagers created the whip to spear it and drag it to the ground. The whip, along with other information on aswang and Pacific Island monsters, was written in a book created by a Spanish missionary who had spent time in the Philippines.
In 2011, the Winchesters and Bobby Singer encountered an aswang named Jason in Nevada. Bobby contacted Marta who had come into possession of the missionary's book and was capable of creating the whip. Having made a deal with Jason, a nest of vampires attacked the hunters and unsuccessfully tried to kill them. After the attack, Marta was able to complete the whip.
After tracking Jason to his lair in a mine, Sam managed to throw the whip around him before wrapping it around his own shoulders and chest and tying it as best he could to prevent losing hold of it. In response, Jason took off, dragging Sam by the whip which he refused to let go of. Jason used the whip to slam Sam against granite boulders in an attempt to kill him, but as Bobby fired at the aswang with his rifle, Dean grabbed onto the whip above Sam and used his added weight and strength to help Sam drag Jason to the ground. While the Winchesters, joined by Bobby, pulled Jason towards the ground, he attempted to tear out the stingray barb without success as the spices on the whip burned his hands.
Finally, after pulling the aswang to the ground, Sam and Bobby struggled to hold it down while Dean grabbed the barb and dragged it down through the aswang's flesh, tearing through the stomach. Dean used the barb to tear open Jason's torso, exposing his heart. Dean yanked the barb upward and then twisted it when the barb caught on the rib cage. Dean finally pierced the aswang's heart with the stingray barb of the whip, causing the heart to burst open and spew black fluid over all of them. The heart then caught fire followed by the rest of Jason's body and he burned to ash.
With Jason dead, Dean led the others to where he had discovered the aswang's eggs. With the eggs proving otherwise impervious to harm, Sam pierced each one with the whip's stingray barb, destroying them and preventing the eggs from ever hatching.
The whip is made out of two parts hemp and one part seaweed with a stingray barb on the end. It has to be steeped in a mixture of spices including cinnamon, cardamom, vinegar, salt, ajowan, galangal, screw pine, tamarind, wattle seed, kokum, kaffir lime and lovage. After it is steeped in the spice mixture, the whip has to have an enchantment placed upon it. The ritual involves drawing a symbol on the floor of the room with candles lit at the cardinal points. Once the whip is ready, it has to be placed in a brass bowl at the center of the symbol and a Latin incantation read over it. At the end of the incantation, the caster throws a powder into the pot, causing flames to engulf the whip which simmers, blackens and releases a fragrent mix of spices. Once the flames disappear, the whip is ready.
Once complete, the whip is capable of harming and even killing an aswang if the stingray barb pierces the creature's heart. Though aswang eggs are invulnerable to other means of harm, the whip can destroy them as well simply by piercing the eggs with the barb.