Gogo copies exactly what was printed on the original creature, with the listed exception (unless that creature is copying something else or is a token; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or any Auras or Equipment attached to it, or any non-copy effects that have changed its types, color, power and toughness, and so on.

If the copied creature has {X} in its mana cost, X is 0.

If the copied creature is a token, Gogo copies the original characteristics of that token as stated by the effect that created the token, with the listed exception.

If Gogo copies a legendary creature, Gogo will also be legendary, but because its name remains Gogo, Mysterious Mime, the "legend rule" won't cause either of them to be put into the graveyard.

If the copied creature is copying something else, then Gogo becomes a copy of whatever that creature is copying, with the listed exception.