It seems to me like your dog loves to play with new toys, obviously. My dog does this sometimes whenever he gets out a stuffed animal. However, he doesn't attack any dogs.
A lot of dogs like to be aggressive when playing with a toy because they're having fun, or they want to rip it into pieces.
Your dog most likely wants the toy to himself, or it could be that your dog is playing, (very aggressively) but I doubt it's that.
I would recommend talking to a vet about the problem.
And the dog may eventually come out of the habit. If you have any other dogs in your house and your dog attacks them when they come near the dog while he is playing with a new toy, and he bites them. Then when the dog gets a new toy, you should give the other dogs a new toy as well so they are busy with their own toys.
Hope I helped, and wish ya luck!