in its mana cost, X is considered to be 0.Phantasmal Image copies a creature for two mana, making it an efficient way to reuse a valuable entry ability or match a strong body already on the battlefield. It can copy your creature or an opponent's, but it becomes an Illusion in addition to its other types and gains a sacrifice trigger whenever it becomes the target of a spell or ability.
That fragility is less costly when the copied creature immediately supplies value. Copying Solemn Simulacrum can search for a land, while a larger entry-based threat may provide an answer or cards before anyone targets the Image. The entry choice itself does not target, so hexproof on the creature you want to copy does not automatically prevent that choice.
The sacrifice trigger does not care who targeted it. Your own equip ability, targeted protection spell, or targeted counter placement can also cause the Image to be sacrificed. Indestructible does not prevent a sacrifice, so copying an indestructible creature does not remove this weakness. Counters and attached Equipment on the original are not copied either. Legendary creatures bring the normal legend rule into consideration if you already control another permanent with that name. Choose the copy for what it will actually contribute immediately or through untargeted support. The low mana cost can make a temporary copy a good exchange even when you do not expect it to remain on the battlefield for long.
