While I'm here I might as well do some entries
Garchomp (Alpha Sapphire): It flies at speeds equal to that of a fighter plane. It never allows its prey to escape. Garchomp gets Arena Trap
Cloyster (Pokemon Y):
Its shell is extremely hard. It cannot be shattered, even with a bomb. The shell opens only when it is attacking
Cloyster gets Bulletproof
Now, I personally am a fan of these. They give a decently powerful buff to semi-underused Pokemon without breaking them.
Also, I'll be making a few to try to keep the good ideas flowing.
Accelgor:
Pokemon Black Dex Entry said:
When its body dries out, it weakens. So, to prevent dehydration, it wraps itself in many layers of thin membrane.
This was the best entry I could find. I try to stick to the generation of origin for effects, as they are, in my opinion, the purest to the Pokemon's design and intentions, as well as not filling up on ridiculous fluff. As for the effect:
Accelgor gains Dry Skin.
This increases Accelgor's use by giving Rain Teams a semi-strong, fast option to punch holes into opposing teams, and perhaps sweep later on thanks to Dry Skin increasing its longevity, and also negating Life Orb recoil for Accelgor.
Well, I didn't have enough time as I thought for this. I'll add more in later.