Complex sentence: The winners of the first phase are split up into separate genders--three guys and three girls--each player for themselves, and have to race down a slippery tarp into water, then back up a sand dune.
Split into simpler sentences: The winners of the first phase are split up into separate genders--three guys and three girls--each player for themselves, and the second phase is a race through a sand dune course. The remaining players have to race down a slippery tarp into water, then back up a sand dune.