Yenna, Redtooth Regent

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

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

If something becomes a copy of the token, the copy also isn't legendary.

Except for the listed exceptions, the token copies exactly what was printed on the original enchantment and nothing else (unless that enchantment is itself copying something else; see below). It doesn't copy whether that permanent is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

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