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

If Mirror Mockery enchants a creature you don’t control, and you are the defending player, you can block with the token.

Notably, the token won’t be attacking.

If Mirror Mockery’s ability creates multiple tokens (due to an effect such as the one Doubling Season creates), all such tokens will be exiled by the delayed triggered ability.

If the copied creature is a token, the token created by Mirror Mockery copies the original characteristics of that token as stated by the effect that put the token onto the battlefield.

The ability that exiles the token will trigger at end of combat no matter what happens to the original creature or to Mirror Mockery.

If Mirror Mockery is no longer on the battlefield as its triggered ability resolves, its ability makes a copy of the creature it was enchanting when it left the battlefield. If it left the battlefield because it was no longer enchanting a legal creature, it makes a copy of the creature it was most recently enchanting before it left the battlefield.

If the copied creature is copying something else, then the token enters the battlefield as whatever that creature copied.

A token that enters the battlefield as a copy of a face-down creature is a face-up colorless 2/2 creature with no name, abilities, or creature types.

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

The token copies exactly what was printed on the original creature and nothing else (unless that permanent 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, and so on.