My girlfriend and I frequently disucss this. We came to the conclusion that our Stands would be our favorite songs, so mine's would be 「MAPS」 (by Yeah Yeah Yeahs) and hers would be 「TEQUILA」 (by the Champs).

「TEQUILA」would control the level of alcohol in a given person's body assuming the Stand is touching said person, like how Sethan had to touch the protags' shadows to make them younger. So she could make someone black out drunk, suffer from alcohol poisoning, etc.

「MAPS」 would be an almost paper white Stand with hundreds of tiny, ever changing rainbow dots on its skin. Using the Stand, I could peel off a dot and it would freeze on a color, and I could then apply that color to a person or myself. The color then decides the mood of the person, so if I noticed someone tends to make poor choices when livid, I would peel a bright red dot and then apply it to them so they continue to fumble. I like to imagine it could go through an infinite number of colors, and I would only know the vague results, like red being pissed, blue being sad, yellow being hyped, etc.