It is the Pokemon of Malice, God of Anti-Matter, ruler of the Distortion World, Giratina! 
And he's very bloated as well! 
Since he discovered the delightful Poké Puffs, he has forsaken his revenge plans against Arceus, Dialga and Palkia to gorge himself on these treats! 
He doesn't care about his weight, all he cares for is the pleasure of eating. 
He's irritable and malicious, though he's also very clumsy and goofy due to his weight, ending up as a pathetic mess.
Just feed him to please him!