Thanks.
The best part about writing custom powers is the part where, weeks or months later, something that would be problematic is easily modelled with what you wrote before.
As for harpies, somebody suggested using Goblin stats and adding Wings
here. But that wouldn't really fit your request, so here goes:
Harpy (Feet In The Water)
High Concept: Harpy
Other Aspects: Filthy Creature, Daughter Of Poseidon, Divine Punishment
Skills:Good: Intimidation, Fists, Athletics
Fair: Lore, Conviction, Discipline
Average: Endurance, Might, Presence, Deceit, Survival
Stunts:Maddening Screech (Intimidation): Given a chance to scream at someone constantly for a long time, can use Intimidation to make mental attacks.
Powers:Aquatic [-1]
Wings [-1]
Claws [-1]
Inhuman Speed [-2]
Ritual (Weather Control) [-2]
Total Refresh Cost:-8
Refresh Total:-2