Rulings

If the copied creature has {X} in its mana cost, X is 0.
If the copied creature is copying something else, then the token enters as whatever that creature copied (with the listed exception).
The token 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 creature copied by the token had any "when [this creature] enters" abilities, the token also has those abilities, and they'll trigger when it's created. Similarly, any "as [this creature] enters" or "[this creature] enters with" abilities that the token has copied will also work.
If the copied creature is a token, the new token that's created copies the original characteristics of that token as stated by the effect that created the token.