If multiple creatures enter the battlefield at the same time, Evolving Adaptive's ability may trigger multiple times, although the stat comparison will take place each time one of those abilities tries to resolve. For example, if you control an Evolving Adaptive with two oil counters on it and two 3/3 creatures enter the battlefield, the ability will trigger twice. The first ability will resolve and put an oil counter on Evolving Adaptive. When the second ability tries to resolve, neither the power nor the toughness of the new creature is greater than that of Evolving Adaptive, so that ability does nothing.