Leafeon

Because its cells are very similar to those of a plant's, Leafeon can perform photosynthesis.  In fact, when you see one sleeping in a patch of sunshine, it's using photosynthesis to produce clean air, and therefore, is always enveloped in clear air.
Leafeon is the Grass-Type Eeveelution.  It is an okay Pokemon.  It has low Sp. Attack, Sp. Defense, and HP stats.  It has okay Speed stats, but Leafeon is geared toward Attack and Defense stats.  Although more of Leafeon's moves are Physical than Special, not all the Physical moves are good.  I mean, if it didn't have low Sp. Attack stats, you could give it Giga Drain and it would have more power than it is now with lower Sp. Attack stats.  However, Leafeon does have some good Physical attacks.  For example, Leaf Blade, X-Scissor, Last Resort, Giga Impact, Dig, Retaliate, and maybe Aerial Ace if you have a Life Orb or a Sky Plate on Leafeon.  You might also want to use Swords Dance to become a powerful Leafeon.
Leafeon's ability is Leaf Guard.  If you have a status condition such as Burn, Paralysis, Poisoning, all that stuff.  Anyway, if you have a status problem, it will be healed in Sunny weather conditions.  So if you want, you could use Sunny Day to be safe.  It's a decent ability.  It doesn't have any flaws or anything.
So Leafeon might not the best Eeveelution, but it isn't too bad.  I just don't see too many people using Leafeon these days.