Hat:
Color is off. The counterfeit's hat is a brighter green, while the official plush is more muted. Also, it appears that the bill of the cap on the counterfeit does not have the soft material on top attached well to the felt on bottom, so it may separate a bit. The detail on the "L" is also not quite as well done on the counterfeit.
Hang string:
The counterfeit has a thicker white string with a suction cup attached (very few official UFO catcher plushes feature suction cups). The official plush has a thin but sturdy white string.
Tush tag:
The tush tag is an exact copy of the official plush, however, the counterfeit is printed on slightly smoother fabric, and the printing is a bit heavier and more prone to blurring (especially on the kanji).
Hang tag:
The hang tag is also an exact copy of the one from the official plush, though the one on the counterfeit is printed on slightly heavier paper. The biggest difference here is the way that it is attached to the plush. On the counterfeit, the hang tag is attached to the ear, while on the official plush, it is looped through the tush tag.
Face:
The angle of the face seems to differ, along with the size of the mustache. The counterfeit is angled down more (he does have a mouth, though you can't see it in the picture), and the mustache is a bit larger and covers up some of the mouth.
Arms:
In the official plush, Luigi is supposed to have his hands behind his back, but in the counterfeit, they seem to be more down at his sides. The cuffs also seem to have a harder time staying in place on the counterfeit.
Body:
As a whole, the counterfeit looks a bit stockier than the official plush. Embroidery on the button is not as well done.
Card:
Due to the incorrect arm placement on the counterfeit, the card will also be at a different angle. On the official plush, you can clearly see both A's on the Ace, but on the counterfeit, the bottom one is obscured. Also, the back of the card is printed differently. On the official card, the back of the card is red print on the white fabric, while the counterfeit seems to be white print on red fabric.
Easiest ways to compare:
Suction cup is a dead give-away, as well as the way that the hang tag is attached.
