Keldeo

Based off of a kelpie or a unicorn, it (genderless) has an alternate form (resolute) when it obtains the move secret sword by move tutoring. It is the latest addition (and the youngest member) of the swords of justice. Brony squad. Yes.^ω^) (　^ω^)
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Ok... P.S He's a myhtical pokemon. (MOI FAVOURITE) He debuted in the 15th pokemon movie; Kyurem vs Swords of justice. (base stat total: 580)
Let's see what bulbapedia has to say...
Keldeo is a quadruped, colt-like Pokémon with a cream-colored body. 
It has a short, rounded snout with large nostrils, and blue eyes. It has
 a large, feathery red mane, long, dark blue, ridged eyebrow-like 
protrusions, and a single cream-colored horn that curves slightly. The 
back of its head, as well as its neck, is covered with fluffy, light 
blue fur. Keldeo has blue hooves, which are capable of ejecting water. 
Its tail is light blue with white spots and resembles an elaborate 
feather in a cap.
Upon learning Secret Sword in Pledge Grove,
 Keldeo transforms into its Resolute Forme. The dark blue protrusions 
become shorter and lighter in color, resembling ears. Its horn becomes 
dark blue, and grows larger and ridged. On the side of its head are 
three feathers colored aqua blue, green and orange.
Keldeo tends to cross the world, and 
often appears at beautiful watersides. It can walk across water by 
ejecting water from its hooves. It is thought that when Keldeo becomes 
resolute, its body fills with power and it becomes swifter.
Long ago, a fire started in the Moor of Icirrus because of a war among people. In this fire, Keldeo was separated from its parents, but together, Cobalion, Terrakion, and Virizion
 took care of Keldeo. They acted as its parents, and they taught it 
knowledge and moves for survival. Keldeo eventually grew and even 
surpassed the three Pokémon. One day, Keldeo took off from the forest 
with no one knowing why.
When the four meet again, they teach Keldeo the move Secret Sword.