The actor - who plays Bay surf instructor Romeo Smith - told Inside Soap that the episode required long shooting hours and a script nearly double the size of those used for normal shows.
"It involved almost every character on a location shoot!" he said.
"It took a lot of time, so we've been endlessly filming scenes from other episodes to make up for it.
Mitchell added: "My script is much thicker than usual with all the extra pages."
The cliffhanger is due to air later this year on Channel 5.