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[Zelda: Ocarina of Time] What exactly is the Odd Potion?

On the sidequest to get the Biggoron's Sword, you have to deliver an old lady's Odd Potion to that creepy bald guy in the Kokiri Forest. All she says about it is that it "doesn't work on monsters". What did the bald guy want with the potion and what was he doing in the Kokiri Forest?
gpt
The "it doesn't work on monsters" part is probably because she knew he was in the Lost Woods. And anyone who isn't a kokiri will eventually become a Stalfors if they stay there long enough. Even Link eventually became one from getting lost in there after Majora's Mask. 

It's never specified what the Odd Potion is. But Grog seems to find his entire family disgusting. He says he is pretty much the only nice guy around (although agrees that Link must be one after training his Cocco.) and when you are an adult he has removed himself from society all together. The potion would maybe work as an "anti depressant" or something of that nature.