As played by Seth Green, Oz quickly became a valued member ... one of those roles was in the Mob movie "Knockaround Guys," co-starring Vin Diesel and Dennis Hopper. But if he wanted to appear ...

Once you watch the scene where Seth Green leaves Buffy ... left the show to go film Knockaround Guys, a dark comedy starring Dennis Hopper and John Malkovich. Whedon described losing Green ...