That isn't a bad idea for a stand, actually

I think it would be a great stand for an Okuyasu/Polnareff-type ally. Like it would have incredible potential in very specific situations and only if the user remembered to use the right ability at the right time. Or it could create hilarious knock-offs of better abilities.
For example, if it copied Star Platinum: The World, it would only stop time for a blink of an eye. Copying Crazy Diamond would allow it to speed up the target’s natural healing ability. Copying Love Deluxe would allow the user to control their nose hairs. Copying White Snake would allow it to make an 8-track of the Stand’s ability, but not the entire stand. And so on.