Psychology 101, Id is our instinctual desires of food, water, sex, etc and works directly from the pleasure principle. Id wants it and Id wants it now. (Mandra)
Ego is intelligent and serves both Id and Super-Ego. Ego reasons what needs to be done to seek pleasure in the long run. Ego Plans. (Grimwit)
Super-Ego punishes for not staying withing the rules Super-Ego or your parents made. Super-Ego is moral and knows what's right. Super Ego also stands as direct opposite from Id because Id is reckless and walks all over Super-Ego's well thought out code. Super-Ego is honorable (Adria)
Now that that's done, lets talk about Super-Id. Super-Id works on the Death Principle (ie. Fast Ego, Kill Kill). Super-Id has an instinctual desire to cause harm, but not for survival or procreation, and so is not ID. Super-Id, instead stands in direct opposition to Ego, because there is no selfish or moralistic desire for it, so there's no reason involved. Instead, Id adapts to Super-Id and remarks that this MUST work off of pleasure principal because why else would you do it? Super-Id wants you to bleed. (Mr. Brimstone)
As far as I know, Super-Id is an impossible phenomenon in the real world because it would have to assume that humans are naturally evil, however, Natch Evil's grand Star, Saffron C. Sativus, works directly with Super-Id.