Maralen, Fae Ascendant

If Maralen enters at the same time as one or more other Elves or Faeries you control, its first ability will trigger for each of those other Elves and Faeries as well as itself.

If an exiled card has {X} in its mana cost, X is 0 for the purpose of determining its mana value.

Since you are using an alternative cost to cast the spell, you can't pay any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, you must pay those.