That odd potion.

[Chris Schumacher]

From the Moonshade document:
" get a Certificate from the Rangers, break into Torrissio’s manor, battle the automatons, and steal the secret to transforming Fedabiblio. The player is probably expecting to need a spell, and there are many spells here. However, the real secret is a Potion which is on Torrissio’s desk (one of three -- the others are ordinary Potions). (A note in the Apothecary shop identifies the three potions by color and function.)"

I think this might explain what that strange potion is, the one that comes in the brass vial? Whenever you use it, it isn't used up and the Avatar says something like "What is this?!". You can find it several places in the game, most notably in the Mad Mages house.
I remember seeing a "mandrake essence" type potion too, but it didn't seem to do anything.

[Warder]

The mandrake essence thingy restores your mana.

[Kennedy]

Are you talking about the orange glowing potion or the blue swirling potion? I kind of remember there being both in the game. I think there was also orange and blue potions that were for warmth

[Chris Schumacher]

If you mean the odd potion of the title (as opposed to the one which had the same graphics and animation as the Mandrake essence in BG), it's in a brass vial (or phial, if you prefer). It doesn't even look like a potion, though it's often in with other ones. It looks more like an upright oil lamp. I believe that both the Mad Mage and the apothecary guy in Moonshade have ones in their collection. The Mad Mage has one for certain. It's description is simply "potion".

[Chris Schumacher]

Nix that, I just looked and the potion wasn't in either places. Does anyone
remember where that really strange potion is? Maybe it's in Vasculio's lab.

[Kagehi Kossori]

There is on in a box on the cat island you have to use the map teleport cheat to get to. I have no idea where in the regular game it is.

[MV]

I found one in the naked chick cave in a chest that is next to a cheerleader statue.

It almost looks like a giant brass thumbtack.

I don't know what it does though.

[Crowley]

That potion can pop up in Torrissio's and Gustacio's laboratories when they fiddle around and set potions on the tables. I'm not sure, but I think Vasel also does that in Erstam's lab.

[Chris Schumacher]

Does anyone have a savegame post-Banes when whathisface is still a statue? If that IS the potion that is supposed to reverse calcification, I'm betting that the developers didn't bother to remove the effect from the code (if it were ever implemented).
Speaking of which, since in the original version the Philander's Friend didn't turn people back from stone, it might explain just what it was supposed to
be. I mean, think about it: the name, that way it's shaped?
BG: I took this old wand I had and modified it to alter blackrock. The damn thing doesn't work, though!
SI: I took this old wand I had and modified it to---
(post terminated)

[MV]

Just tried, nope, he's still a statue. But now a statue with a brown liquid spill at his feet.

[Chris Schumacher]

>Just tried, nope, he's still a statue. But now a statue with a brown liquid spill >at his feet.

Ah, so now we know. It's a laxative.