Using a regular small flash, the flash duration is short enough to freeze pretty much anything within reason at pretty much any flash power, as long as you have little or no ambient light getting through. Really fast moving objects, like hummingbirds, will require a lower flash power to get a shorter flash duration, but that's the exception rather than the rule. For most practical purposes, the flash duration itself doesn't matter much.
Most of the time, ghosting comes from the ambient light. The flash sync speed on most cameras is too slow to freeze a lot of action if there's much ambient light. Your ambient will need to be at least a couple of stops lower than the flash to control the ghosting. In most shots where the motion is frozen by flash, the subject is either against a (mostly) dark background, or the background is lit by flash too. If the background is lit by ambient light, there will be ghosting against the background.
Do you have an example of what you're trying to do?
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