Dark Wish

After a warlock leaves a fiendish patron there is a chance of this feat appearing, at the DM's choice. 
A mark appears somewhere on your body, it appears to be made in dead/burned flesh in the shape of either a rune circle or a personal crest from your previous patron. The mark is surrounded by seven five pointed stars. This mark grants the ability to use the wish spell once every three days as your patron attempts to lure you back to them. There are a maximum of seven wishes available in the brand, one for each star. As a spell is used a star will vanish. Once all the stars are gone the brand vanishes, often with the smell of sulfur and burned flesh.