At three and a half months old, you would think that teething is the reason, but you seem to portray him as being aggressive and biting to harm, not to teethe. I am stumped as to why such a young puppy would even know to be mean spirited like that.
Have you consulted with your vet? There may be some painful reason why Yoshi is being so mouthy. There are many many threads here about biting. If you do a search on it, you may find some interesting and helpful answers. I am sure other folks would suggest consulting a dog behaviorist as well.
I wish you the best of luck with this problem, and wish I could be more helpful, but I have never had to personally deal with this. My pup bites me all the time in play, and we have been working on "NO bite", but she doesn't have a mean bone in her body so I can't help with the aggression.
Good luck!