How can I make my puppy stop biting, pulling hair, and scratching me without hurting him physically or scaring him off mentally?
You want to prevent these behaviours because reacting in any way will mostly act as a reinforcer.
The usual issue with a puppy biting is them feeling the need to do that as a way to communicate to you that they’re..
Feeling bored: If your pup is awake, that’s their first indicator that they’re ready to go and do things! Biting is usually an indicator that they might’ve been waiting for a bit too long or that the activities they’ve gotten to do need something more. Mental enrichment is what most pet parents I know don’t really practice. I would start there.
Feeling overexcited: in which case you can provide their nose with a scent/treat to help guide their mind towards a different activity like a tug and pull game, before a mental stimulation exercise and end with a frozen Kong or licky mat to help my dog soothe, mellow and get ready to sleep. :)