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Chosen answer: There is nothing in the story to suggest what the "goo" is so we can only summarize that this is simply the remains of the master after his execution. Why he would become "slime" is debatable but as the air of Skaro created the Dalek Race, it is fair to assume that a prolonged exposure also mutated the Master's body in some way.

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Chosen answer: A very good question - It is suggested by Paul McGann during the introduction that "rules mean nothing" to the Master. Assuming this to be the case, that would suggest that outside of Galifrey where a Time Lord's life is absolute, The Master would be able to "alter and cheat" time.

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Chosen answer: A good question, and one that is posed by the characters themselves several times. It is feasible that the doctor having already been to that time already is aware of what may happen to them, and as he is at this point also able to travel to parallel points in time, may have also seen what may happen if they change events - which is presumably for the better.

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Chosen answer: Whereas Grace and Chang are both human, Captain Jack Harkness is alien - So the effect the TARDIS has is very different. In addition, as is revealed in the series as well, The TARDIS is more than a machine, it is alive... It also has knowledge even the Time Lords do not have - By making Jack Harkness immortal, it is also fulfilling his destiny.

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