The clip, released Monday, explores how Deadpool (Reynolds) has captured Savage in order to present to him a PG-13 version of the originally R-rated Deadpool 2.
The set up pays homage to Savage's role in 1987's The Princess Bride where the actor, as a young boy, was told a bedtime story.
"You're in a PG-13 version of Deadpool, filtered through the prism of childlike innocence," Deadpool says to Savage, who is taped to a bed. "And nobody does childlike innocence like you Fred. Nobody."
Deadpool is also seen confronting an elderly couple about how they remind him of the Disney and Pixar film Up.
Once Upon a Deadpool will feature new scenes added to Deadpool 2 including more banter between the titular hero and Savage. It will be available in theaters from Dec. 12 to Dec. 24. For every ticket sold for the film, $1 will be donated to the temporarily renamed Fudge Cancer charity.