Constantine, produced in 2005, is an action-horro film that revolves around a man named John Constantine, who tries to save himself from going to Hell by exorcising demons in the human world. After a series of event, he learns about the proxy war between the angels and demons, and thus his journey to stop the devils from succeeding.
In the midst of character design, other than the demons that could fly, there was another unique character called the Vermin Man. Made up of snakes, rats, crabs and many types of bugs, the Vermin Man can be formed when different animals and bugs colonize and forms a human-like creature. The initial concept was slowly designed and finalised and different studios were responsible for the Vermin Man.
Image shows the 2d art concept for Vermin Man, before artists actually produced a real mask for the actor to wear and interact with Keanu Reeves in the shots.
Just by animating the different characteristic of each bugs,snakes or rats is already tedious, but the VFX artists also have to make out how the bugs makes the face of the Vermin Man to show his expression in the scene. The complexity of how Vermin Man looks, how he acts and fights took more than 1 year for the VFX teams to create.
After all, in the film, Vermin Man is replaced into a full CG character so this allowed more flexibility to the VFX teams to work on.