You had been hiking under an old stone bridge when you came across an even older wooden box half-buried under some dirt near the water.
Digging out the old box with your fingers and lifting it up, you open it to find two strange glowing vials, one filled with purple liquid, the other filled with a bright green. In shock, startled by the warm glow of the two vials, your eyes set upon an old yellowed note written in cursive. Appears to be instructions of a cryptic nature.
The note reads:
For changing beasts to man and man to beasts.
The more you give, the more it will change. Put it back and watch it refill. Wears off after a time.
Purple: To make a beast more of a man. When it turns back, its mind will not fade. Beware of this!
Green: Add the hair of the creature to be and let a man drink for effect. Don't add hair for a surprise!
Wide eyed, you put the note back, close the box, and put it in your pack. You head for home, kind of spooked, and on the way you wonder if it really works.