it is very good that you are cautious about this, my suggestion would be to let the puppy boxer be around the bigger one a little more each day just to introduce each other, and make sure they are monitored by a person that can separate them if things get out of hand. when they first meet, the elder dog might be a little aggressive towards the smaller dog to show its dominance, and place in the pack. you see, all dogs want to do is be part of a pack, and live that way. From a young age, dogs engage in play with one another. Dog play is made up primarily of mock fights. It is believed that this behavior, which is most common in puppies, is training for important behaviors later in life. Research on puppy play has shown that puppies do not engage equally in both dominant and submissive roles in fights; rather, puppies will tend to start play fights with weaker puppies they believe they can dominate . Additionally, puppies will intervene in play engaged by other pairs. In these situations, the puppies overwhelmingly aid the dominant dog. Puppies do not show reciprocity in interventions, suggesting that they prefer to be dominant in a fight, and are being opportunistic in the short-term. In the long-term, intervention may aid the puppies in learning coordination.
A common behavior among domesticated dogs, is chasing their own tails. Researchers are not completely certain why dogs chase their own tail, however some research studies found a link between tail chasing and high cholesterol. A study found that when dogs experience an increase in activity of hormones tied to the "fight or flight" response caused dogs to chase their tails more often