You must choose an existing creature type, such as Human or Warrior. Card types such as artifact and supertypes such as legendary can't be chosen.

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

If the nontoken creature leaves the battlefield before Molten Echoes's triggered ability resolves, the token that's created uses the creature's last known information from before it left.

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

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.

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