Cirque du Soleil for the first time is offering a buy one ticket, get the second one for $15 deal for six of its Las Vegas-based productions: “Ka” at MGM Grand, “Mystere” at Treasure Island, “Zumanity” at New York-New York, “Zarkana” at Aria, “The Beatles Love” at the Mirage and “Criss Angel Believe” at the Luxor. The BOGO offers are available only for performances through Dec. 17, so buyers must purchase the first ticket at full price by Dec. 17 in order to get the second ticket for $15.