The Deathless Frenzy was a bio-weapon created by Dr. Didier Ines. When given to a subject, it would cause them to go into an unstoppable blind rage. Yelena Belova tried to keep Natasha Romanoff from retrieving the Endless Fury serum but failed. Natasha brought the doctor to a lab in Zurich and ordered him to develop a vaccine.
Yelena attacked the army of General Khan, hoping to destroy the canisters of the Deathless Frenzy before being used against the U.S. and Russian armies, but she failed. Dr. Ines, though unable to develop a cure, was able to develop a vaccine which was transported to Rhapastan. The serum was going to be used by General Khan on his army to create an invincible army against U.S. and Russian soldiers. However, the soldiers of General Khan were tricked by Natasha into being inoculated with the vaccine for the Deathless Frenzy. During the battle, the serum failed to produce the desired effect, but General Khan, not being inoculated, began feeling the effects of the drug. The Black Widow was able to stop the frenzied General Khan, who later died as an effect of the drug.