It’s possible to win even with 2 harpies, but it depends on the damage RNG, so I decided to leave only one; in this case, we don’t take any damage at all.
This only works if the harpy occupies the central cell; the problem is that you need to manage to make it do so. It also worked this way, but it’s more complicated: https://imgur.com/a/muiuf
In principle, this can also be considered an exploit, but if you fix everything, the game might not be as interesting.