The actor - who plays Rudy on the E4 drama - told SFX that he is yet to see scripts for the new episodes.
"I'm properly looking forward to it this year and the storyline is always f**king hilarious," he said. "[Series creator] Howard [Overman] is just a fricking genius."
He added: "[I don't know] b*llocks. Literally, they don't trust me. I don't blame them neither. It's a case of wait and see, really.
"I'm sure it'll be disgusting and completely outrageous. And it'll have an effect on the people that watch it."
Misfits will introduce three new regular characters, following the departures of Iwan Rheon (Simon) and Antonia Thomas (Alisha).
"I don't know who's playing them," said Gilgun. "I've no doubt they'll be exceptional people.
"The casting people... do know what they're doing and they don't want to f**k up and let the the audience down because it's got a massive following."
Misfits was officially picked up for a fourth year in December.
The series will return to E4 in late 2012.
> Misfits Joe Gilgun: 'Series four will have a fresh outlook'
Watch the Misfits cast discuss the last series below: