Jake Johnson ("New Girl") and Damon Wayans Jr. ("Happy Endings") star as two best friends who decide to impersonate cops for kicks but find themselves in over their heads when they unknowingly mess with a real mobster.
Greenfield ("The Girl Next Door") wrote the script with Nick Thomas, and the director will also produce with Simon Kinberg of Genre Films. Production will begin shortly.
Key is currently working out scheduling and his role is being kept under wraps for now.
A standout performer on "MADtv," Key has appeared in a handful of studio comedies over the years including WB's "Due Date," Sony's "Just Go With It" and Universal's "Role Models," which coincidentally, was initially developed by Greenfield before David Wain stepped in to direct.
Key, who serves as a writer and executive producer in addition to starring opposite Jordan Peele on Comedy Central's hit "Key and Peele" show, will soon be seen in a pair of Sundance comedies — Millennium Entertainment's "Hell Baby" and Jill Soloway's "Afternoon Delight." He's repped by UTA and Principato-Young Entertainment.