To choose a creature type, you must choose an existing creature type, such as Vampire or Knight. You can't choose multiple creature types, such as "Vampire Knight." Card types such as artifact can't be chosen, nor can subtypes that aren't creature types, such as Jace, Vehicle, or Treasure.

Replacement effects that modify creatures of a certain type as they enter will apply after you apply this effect. For example, if Warrior is the chosen creature type and you control Bramblewood Paragon, a Runeclaw Bear would enter the battlefield with an additional +1/+1 counter.