Maybe a bit of an esoteric question, but how do you make hags interesting, especially powerful ones?
Give them abilities beyond what is present on their statblock. Granted, most Hags have PLENTY enough in their stats to make them interesting, intimidating, and tricky foes--especially when there's more than one!--but if you want to make them more terrifying, giving them access to powers no player could ever reach or conceive of is a surefire way to make them spooky.
One can simply look at the popular depictions of Green Hags; on the tabletop proper, they're among the weakest and most simple of all Hags. You wouldn't think so if you've ever seen, say, specific stretches of Critical Role or a certain foe in Baldur's Gate 3, though, which show just what happens when a Green Hag becomes ambitious enough to reach for more power. In Pathfinder, a Hag is a person who has purged their soul of the capacity for Good, leaving them as close to pure Evil as any demon, devil, or daemon, so of course they would be willing to undertake rituals even more depraved and vile if it means increasing their power.
A powerful Hag may have the ability to conjure illusions without needing to make any spellcasting gestures, manipulate all the objects in her hut with a thought, control the environment around her home as easily as she could move her own limbs, ensnare the minds of the weak or the beastly and verminous, or manipulate the party's magic or luck.
