Sea Guardian Duo: Phione & Manaphy

The second duo released in the Sinnoh Generation are the Sea Guardians, Manaphy and Phione. Both Pokemon are consider to be Mythical, but there is much conversation about the status with Phione. It doesn't really have the stats that a Legendary Pokemon does, and there have been a number of evidence that both supports and disputes this status for it. Regardless, Phione is still considered to be a Mythical Pokemon to this day.

The duo resembles the Mew Duo from the first generation, as their is a sort of parent within each duo. Mew's DNA was cloned into Mewtwo, while Manaphy must breed to make a Phione (they are the only Pokemon known to breed within the Games).

As for where competitive play goes, Manaphy is superior in every single way. On top of being the fourth straight 100 Base for each of it's stats (like Mew, Celebi, and Jirachi), it also has access to the somewhat exclusive move of Tail Glow. This moves allows it to sharply increase its Special Attack, multiply the stat by 2.5 in just one move (x4 maximum increase in two moves).

Phione, however, doesn't have all the same perks as its parent. It doesn't have a straight 100 Base for all of its stat categories, but a straight, non-impressive 80 Base stat for each category. And it doesn't even receive Tail Glow, which it so desparately needs.

#489 - Phione: The thing about Phione is it can actually be found in all the mainstream Pokemon Games from the fourth generation moving forward, since all you have to do is breed another Phione or Manaphy to get one.

#490 - Manaphy: Unlike Phione, Manaphy can't be found in every game since its release; it actually can't be found in-game in any this that time. Manaphy is a Mythical Pokemon, which means it can only be obtained by a Pokemon Event.