See Ya Later Gladiator is a 1968 Warner Bros. Looney Tunes cartoon directed by Alex Lovy.
[1] The short was released on June 29, 1968, and stars Daffy Duck and Speedy Gonzales.
There, they offend a centurion who sends them to the lions as entertainment for Emperor Nero in a gladiator arena.
Back in the present timeline, the scientist discovers Daffy and Speedy being chased by a furious Nero.
The cartoon features a slightly different arrangement of "The Merry-Go-Round Broke Down" by Bill Lava (the second being 3 Ring Wing-Ding.)