I do hope Venom gets a sequel for no other reason than to finally see Carnage on the big screen. However Carnage only works if it's an 18 and not the PG rubbish we have with Venom. I'd put money on a uncut version of Venom coming out on Blu Ray just after Christmas.
My only knowledge of Carnage is a single page from a comic where he's strapped down in prison or in transit and he cuts his tongue on one of his sharpened teeth so he can activate his crazy mode. Pretty neat.
Carnage is crazy offspring of venom which is used by a serial killer. Back in the 90s the comic (and game) Maximum Carnage saw Carnage gather some villians and have some fun, Spider-Man and Venom teamed up with Cap and others to stop them.a brilliant story and amazing art work.
Carnage is much like the Joker as he makes the heroes think about how far they will go to stop him.