Why is my puppy thin, has stinky loose poop, and bites frequently?

Congratulations on your new puppy! Mylo is adorable! From the photos, he looks like he is in good condition, however, he may actually be thinner than he appears because he is so fluffy. You should be able to feel his ribs and spine, but they should be covered by muscle and fat. Essentially, you should feel bones with a slight amount of pressure, but not when only running your hands over him. Loose feces is common in puppies, but should be evaluated by a vet. It can be caused by intestinal parasites, inappropriate or quick diet changes, I recommend having Mylo seen by a vet as soon as possible, you can bring a fecal sample with you in a disposable container so your vet can test for parasites. Regarding Mylo's biting, this is very common in puppies as they are teething. It is a behavior that is undesirable and can be trained out. When Mylo bites, I recommend ignoring him and stopping what you are doing. This will let him know that the behavior is unacceptable, and that he can only have your attention when he is not biting. I hope this helps and am happy to answer any other questions you may have!