So a while back ago as a noob player i played L4D2 with this mod, i randomly clicked buttons until i got one, it was a mutation where the survivors randomly each some seconds their guns changed, i remember this but not its actual name, i need help, since it was the best experience ive ever had, i literally remember going from a M60 to a grenade launcher and kicking the ass of a tank, please someone tell me how is it called