I know y'all say Hey Ya! doens't really have the power to grant good luck, but I find it odd that at around the same time Pocoloco gets informed of his good luck, Hey Ya! appears. Not to mention that Hey Ya! seems to know the future, and informs his user of his abilities. In other words, by trusting what Hey Ya! says, Pocoloco experiences the best outcome and the maximization of his luck. I am going out on a limb and saying that Hey Ya! is one of the most powerful stands in the series, if only because it's paired up with Pocoloco.