The much-travelled striker had two spells with the Linnets, rejoining the club in January after a short stint with EVO-STIK League West Division rivals Glossop North End.
Colwyn Bay resigned from the NPL after the campaign just ended to move into the Welsh non-league pyramid. They are preparing for life in the FAW Championship North & Mid, part of its second tier.
Runcorn Linnets manager Michael Ellison said: "Mitch has been great for us over the past couple of seasons on and off the pitch - scoring some really important goals for us in our title- winning season and also this season, very nearly helping us into the play-offs at the first attempt
"He’s a top lad to have around the changing rooms and will be missed."
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