Defeat 180 beasts?

For this kind of quest (Quest that have cooldown skill involve), you could use The double Blink fox Method to bypass the cooldown.

You can now summon fish every turn. So Bring Blink Fox, Cookie, A Merc that can deal at least 15 Dmg (So you can kill a fish every turn.) In this specific task you don’t have to spare the Mad summoner as cookie will summon fish as enemy for you, just don’t kill the last fish.