What are the physical traits of Puck in Midsummer Night's Dream?
There is no extended description of Puck in Midsummer Night's Dream. Since this is a play, description is not necessary, such as it is in a narrative story (novel, short story).
Puck is described by the Fairy in Act II, Scene 1 of Midsummer Night's Dream as a sprite fairy. A sprite is a particular species of fairy that has a human form, pointed ears, sparkly fairy dust and gossamer wings (think of Tinker Bell in Peter Pan). Though possessing beautiful features, Puck loves a good laugh at humans' expense.
Puck is also a shape-changer. He claims to change his shape into that of a "three-foot stool" and then whisk away so the human attempting to sit on the stool falls on the floor instead. He also claims to change to the shape of a "crab" and to impersonate the neighing of a "filly" horse.
He is a mischief maker who likes to pull pranks, though not truly evil ones (nothing worse than skimming the cream from the milk so the wife can churn all day and still get no butter and misleading night-wanderers) and will trade good luck with anyone who will call him Puck or Hobgoblin instead of his real name of Robin Goodfellow, which is an ill-suited name for a sprite fairy who loves pranks and jests.