9/22/2011 : Phantasmal Image's ability doesn't target the chosen creature.
9/22/2011 : Phantasmal Image copies exactly what was printed on the original creature and nothing more (unless that creature is copying something else or is a token; see below). It doesn't copy whether that creature 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, or so on.
9/22/2011 : If the chosen creature has

in its mana cost (such as Primordial Hydra), X is considered to be zero.
9/22/2011 : If the chosen creature is copying something else (for example, if the chosen creature is another Phantasmal Image), then Phantasmal Image enters the battlefield as whatever the chosen creature copied.
9/22/2011 : If the chosen creature is a token, Phantasmal Image copies the original characteristics of that token as stated by the effect that put the token onto the battlefield. Phantasmal Image is not a token.
9/22/2011 : Any enters-the-battlefield abilities of the copied creature will trigger when Phantasmal Image enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the chosen creature will also work.
9/22/2011 : If Phantasmal Image somehow enters the battlefield at the same time as another creature, Phantasmal Image can't become a copy of that creature. You may only choose a creature that's already on the battlefield.
9/22/2011 : You can choose not to copy anything. In that case, Phantasmal Image enters the battlefield as a 0/0 Illusion creature, and is probably put into the graveyard immediately. It doesn't have the ability "When this creature becomes the target of a spell or ability, sacrifice it."