There are many who believe that bad things tend to happen when the planet Mercury is in retrograde. Is there no truth to this or is it a real energetic phenomenon, if perhaps exaggerated as to its influence on things?

There is some truth to this but not for the reasons assumed. It is basically a low-level influence energetically and is of minor consequence with respect to human affairs. As you know, all astrological doings can have an influence on the Earth and its inhabitants to some degree, but this is a very minor example. It can be a cause of mishaps through expectation alone and, in that regard, can cause a nocebo effect which is the expectation in the minds of people that things will get worse and then they do, but it is the person themselves being less cautious or making an error of some kind out of self-expectation that something bad will happen no matter what they do and this actually causes them to be less meticulous and less stringent in their behavior. That is one consequence of such a belief even if it is superstition, but the largest segment of the reinforcement for this astronomical phenomenon being a negative influence is that because humans believe it to be, the Extraterrestrial Alliance will cause their mischief to happen more frequently in conjunction with this sign in the heavens because it will constitute a convenient cover story. This is the same with those phenomena seen in conjunction with a full moon, it is simply that the interlopers use human expectation to schedule their mischievous handiwork because again there will be a prosaic explanation that seems natural, if bizarre, so there will be no further inquiry or questions raised about why things are happening that are unwanted. It is strictly attributed to bad fortune and this serves the interlopers nicely and keeps people in the dark.