Just what's inside there? Is it really mayonnaise? And is it, as the label would suggest, fat free? We may never know. This jar that refuses to open, so obviously powerful and evil that it was voted most likely to be the big bad of a future season, gives special powers to those who hold it. Just like real mayonnaise, though, you can't trust it to be consistent. Today, it might give you the muscle to lop off a demon's head, but tomorrow it might enhance your mystical powers, but it's always handy somehow, which is why an unopenable jar of mayonnaise is soon to be standard equipment among Slayers everywhere.