Hags in Baldur's Gate 3 are dangerous, disturbing, and very powerful. Players can learn this first-hand during Act One, thanks to Auntie Ethel, and while Act Two has other monsters to worry about, the hags come back in Act Three thanks to the quest "Help the Hag Survivors."
Baldur's Gate 3: Avenge the Hag Survivors Quest Guide
Players have more hag business to deal with as they arrive in Baldur's Gate itself.