h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Did not exist untill the 6th edition of the core set of the game, also known as the classic edition. It is very important though, when the mages involved in the game cast a spell or uses some kind of ability, it first goes onto the Stack where the opposing mages are allowed respond to it, after everyone is happy and no more responses are made, the Stack can begin to resolve from the last spell or ability in to the first one. As spells resolve players may add more to the stack. Sorceries cannot be played if unless it is a mages turn, that mages main phase, and the stack is empty, the same is true of lands.
Just thought I would point that out since the existance of it allows for many shinnanagans that were not permitted under the old rules. NO MORE DAMAGE PREVENTION WINDOWS!
The stack helps to simplify those rules some.