When the 2nd MGM opened in 1993 (?) it was a Wizard of Oz theme throughout a great deal of the casino. The whole area after you walked in resembled the yellow brick road. Eventually that was phased out. The Chinese have a superstition about walking through the mouth of a lion and the MGM folks figured that was good enough for them to eliminate that way of getting in!

from the chipguide:

When it opened, the MGM Grand had an extensive Wizard of Oz theme, including the green "Emerald City" color of the building and the decorative use of Wizard of Oz memorabilia. After entering the casino's main entrance, one would find themselves in the Oz Casino facing Emerald City. Dorothy, the Scarecrow, the Tin Man, and the Cowardly Lion were seen in front of the city. The Emerald City attraction featured an elaborate yellow brick road walk-through, complete with the cornfield, apple orchard, and haunted forest, as well as audio-animatronic figures of Dorothy, the Scarecrow, the Tin Man, the Cowardly Lion, and the Wicked Witch of the West. It would end at the door of the city, leading inside for a performance of "The Wizard's Secrets". When MGM Grand began its extensive refurbishment in 1996, the Oz Casino was the first to go.