Any Shiny Pokemon card is Rare. The fact that it is an Entei makes it more so. Of course, It depends on what series the card was from, what edition it is, whether or not it has a special border, and whether or not is has 3-D art or is a special edition. No offense but, you didn't give much detail
Now, it may not have any significant VALUE, But yeah, any Shiny Pokemon card has a much higher rarity than it's normal version (well, there isn't a shiny version of every Pokemon, but for the ones that have one).