It's Not Easy Being Green

"It's Not Easy Being Green" is the sixteenth episode of the third season of Once Upon a Time, and the show's 60th episode overall, which aired on April 6, 2014.

Synopsis
With Rumplestiltskin as her slave, Zelena challenges Regina to a fight to the death and shocks the Evil Queen with the revelation of their familial connection, even while the town lays Neal to rest. Meanwhile, back in the past, in the land of Oz, a jealous Zelena asks the Wizard to send her to Enchanted Forest after discovering she has a sister, Regina, and that Rumplestiltskin is training her to become a powerful force to be reckoned with.

Trivia

 * The Episode title is a reference on "Bein' Green", a 1970 song made famous by Kermit the Frog, who was created and voiced by Jim Henson, whose Muppets properties are part of The Walt Disney Company. Ironically, the studio also produced a 2005 made-for-TV movie based around the Wizard of Oz theme featuring the Muppets, aptly titled The Muppets' Wizard of Oz.
 * The Wizard's figure bore a resemblance to James Franco's character from Oz the Great and Powerful.
 * The silver slippers Zelena wore in the episode are described as the same one featured in the "Wizard of Oz" book.