Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any “as [this creature] enters the battlefield” or “[this creature] enters the battlefield with” abilities of the creature will also work.

If the copied creature has in its mana cost, X is considered to be 0.

If the copied creature is copying something else (for example, if Volrath, the Shapestealer is having its own shape stolen by Hate Mirage), then the token enters the battlefield as whatever that creature copied.

If the copied creature is a token, the token that's created copies the original characteristics of that token as stated by the effect that created the token.

Each token gains haste after it has been created. If something copies one of these tokens, the copy won't have haste, and you won't exile it at the beginning of the next end step.

If one of the two target creatures become illegal, you create one token that's a copy of the one that's still a legal target. You don't create two tokens.

Each token copies exactly what was printed on the original creature and nothing else (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 Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, or so on.