In Resident Evil 6, a number of Neo-Umbrella'sB.O.W.'s emerged from strange cocoon-like objects. These cocoons were actually the result of further C-virus mutation in Neo-Umbrella's J'avo troops, who after receiving so much damage could suddenly mutate further. Their bodies would secrete a slimy substance that would completely envelop them and harden in seconds, forming the Chrysalid. Within minutes or even seconds, the J'avo subject within the Chrysalid would transform into one of several different creatures. These B.O.W.s are referred to as Complete Mutants.
It is also worth noting that not all Chrysalid B.O.W.'s come from J'avo. As demonstrated by Carla Radames, humans injected with a specific strain of the C-virus will immediately mutate into Chrysalids. During the Edonian Civil War, Radames ambushed a squad of BSAA troops led by Chris Redfield and used a bomb-like device to launch several hypodermic needles filled with the C-virus into an enclosed area. Almost the entire squad (Redfield and Piers Nivans were lucky enough to escape) were turned into Chrysalids and emerged from the cocoons as Napads seconds later.