Complex sentence: Original partners included Caesars Palace, Wynn Las Vegas and Bellagio, and in 2009 the event grew to include MGM Grand as an anchor partner and an associate hotel partnership (lower level of partnership) with Mandalay Bay.
Split into simpler sentences: Original partners included Caesars Palace, Wynn Las Vegas and Bellagio. In 2009 the event has grown to include MGM Grand as an anchor partner and an associate hotel partnership (lower level of partnership) with Mandalay Bay.