Shaymin

The flowers on Shaymin's body burst into bloom if it is hugged with love.  It can dissolve toxins and transform a ruined land into a field of flowers in just seconds.
Shaymin is a cute hamster or hedgehog of some sort.  It has a second form, but you need to have an item called the Gracidea Flower to change Shaymin's form.  This item can only be obtained through a special event that's long gone right now, and there doesn't appear that another event like this is happening any time soon.  Anyway, when Shaymin does change forms, it becomes a Grass-and-Flying-Type.  Shaymin's Land form has all of its stats with a base of 100.  Base 100 for HP, Base 100 for Attack, Base 100 for Defense, and so on.  The Sky form has different stats.  This form's stats have a base ranging from 100-127; just including the HP, Attack, Sp. Attack, and Speed stats.  The Defense and Sp. Defense stats have bases of 75.  According to stats, the Land form is the stronger one.
Shaymin has a move exclusive to itself.  It's called Seed Flare, which has a base power of 120.  It may lower the target's Sp. Defense stat by about 3 stages!  Moves that only the Land form can learn are Synthesis, Aromatherapy, and Healing Wish.  The Sky form has moves exclusive to itself as well, which includes Quick Attack, Air Slash, and Leaf Storm.  Otherwise, excluding moves it can only learn from Generation IV, the two forms of Shaymin learn the same moves.  Shaymin has plenty of recovery moves, status condition healing moves, and STAB moves.  This makes Shaymin a somewhat offensive Pokemon.
This Pokemon's ability is Natural Cure.  It heals all status conditions just when you switch out Shaymin.  This includes stuff like Poison, Paralysis, and all of that stuff.  A great ability for keeping Shaymin in battle for a long time.
So the final verdict points to Shaymin being a good Pokemon, whether it's a Staller, or just a Pokemon you use to win battles, this is a Pokemon you should use if you can get your hands on it.