The yellow one

"What does the yellow one do?" You ask and Kruya takes the small bottle out of the case. "It represents the frog's head you found and will change your facial structure when mixed with DNA. If you have read the Harry Potter books, you should know how it works. Take someone's hair, put it in the bottle, drink it down and you'll look like them for a few hours."

You blush and start thinking perverted things, this is hard.