From The Heroes of Might and Magic III wiki

Town: Dungeon

	Attack Skill	6	Damage	1-4
	Defense Skill	6	Health	14
	Speed	9	Shots	0
	Growth	8	Cost	170 gold
Special: Strike and return + No enemy retaliation

[edit] Dwelling

Harpy Hag is recruited in the Upgraded Harpy Loft.

[edit] Upgrading

This is the upgraded version of the Harpy.

[edit] Strategy

Their growth rate is good, they are fast, they attack without retaliation and they can fly: they are ideal for siege battles, especially with expert-level Tactics since this means they will reach their prey on the first turn.

Do cast Bless on them, though: their damage range is huge (1 to 4), so you'd rather they did 4. Especially if they have good morale.