The token copies exactly what is printed on the creature and nothing else (unless that creature is a token or is copying something else; see below). The token doesn't copy whether that creature is tapped or untapped, whether it has any counters on it, whether it has any Auras and/or Equipment attached to it, or any non-copy effects that changed its power, toughness, types, color, and so on.

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

If the target creature is copying something else, the token you create will use the copiable values of the target creature. In most cases, it will be a copy of whatever the target creature is copying. If it's copying a permanent or card with in its mana cost, X is 0.

If the target creature is itself a token, the token created by Littjara Mirrorlake's ability copies the original characteristics of that token as stated by the effect that created it.

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 copied creature will also work.