Giant slugs are very rare, and their corpses are even more rare. I think it's something like you have to kill an average of about 1000 monsters in the druid dungeon to get one, assuming max food preservation. Get acid resist from the ant colony and that's good enough unless you're fighting a threat room of great black wyrms (in which case, throw on a second one, or run for your life).
Yeah, precrowns aren't all that good for beasties. There's too many weapons in the precrown list--maybe half of all precrown gifts will be junk for you. At least your crowning gift is pretty much guaranteed to be good.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.