Witch's Potion

Starting out
Talk to Hetty in Rimmington and tell her to help you become one with your darker side. She will then ask you to get her a burntmeat, an eye of newt, an onion, and a rat's tail. In exchange, she says she will increase your knowledge of the dark arts (Magic).

Collecting the items




Rat's tail
Kill any type and level of rat. There are small, level-2 rats in the house to the south, but you're better off killing the large, level-13 rats to the southeast. They drop raw rat meat which you can use in a later step.

Burntmeat
Take the raw rat meat or any raw meat ((bear, beef, chicken, or ugthanki) and cook it on a fire or range. There is a range in Port Sarim just south of Grum's Gold Exchange. Another is located directly north of Hetty the witch.

If you cook the meat successfully and receive cookedmeat, use the cookedmeat on the fire or range and you'll get burntmeat. You can also kill imps found throughout Gielinor as they drop burntmeat uncommonly.



Eye of newt
Just east of Grum's Gold Exchange in Port Sarim is Betty's Magic Emporium. She sells newt eyes for 3 coins each. If there is no remaining stock, wait for the stock to replenish.



An onion
North of Rimmington between Melzar's Maze and Rimmington mine is an onion patch. Take one.

Finishing up
Head back to Hetty and give her the four items by talking to her. Right-click the cauldron and select "drink from".

Congratulations, quest complete!

Rewards

 * 1 Quest Point
 * Magic experience: $$Level \times 50 + 225$$
 * At level 1: 275 xp
 * At level 99: 5,175 xp