Appropriately enough when Frank is talking about Rocky villains he stops short of Rocky 4 where the villain is Dolph Lundgren who is playing the hero of the fictitious Thundergun series.
Danny Devito and Dolph Lundgren are good friends, which is most likely how they got him to take this role
Dolph Lundgren starred in the Expendables franchise, which also eventually went PG-13 in order to increase theater profits.