“Rivals II” takes our cast of 16 men and 16 women to Thailand for a return to one of The Challenge’s most exciting recent formats. Like every challenge, “Rivals II” requires strength, stamina, and perseverance. But more than ever, it’s going to require mental toughness as each two-person team will be made up of a pair of bitter rivals. The first time around, some rivals were able to overcome their difficulties while other pairs’ animosity deepened amidst the intense competition. And this time, with $350,000 at stake, the pressure is even greater.