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

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

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 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.