Although there are many discrete cultures over the extent and duration of pre-Columbian Mesoamerica, they share a number of regional similarities. Identify and describe at least 3 of these.
As you mention in your question, Mesoamerican civilizations had many things in common with one another. Let us explore some of these commonalities.
One thing that these civilizations had in common was writing systems. Many Mesoamerican civilizations had writing scripts, though historians are not completely sure which society discovered writing first and which societies got their writing systems through cultural diffusion. Not all of the writing systems were similar, but all were written on the same basic kinds of media. Civilizations wrote on stone buildings, on portable objects like pottery, and on codices made of animal skin parchment or paper from bark.
Another thing that these civilizations had in common was the ball game. Ballcourts have been found all over Mesoamerica. Scholars do not really know all of the rules of the ball game or whether rules were common to all civilizations. However, the game was clearly very important to people of all Mesoamerican societies.
Finally, Mesoamerican civilizations all had calendars. These calendars were based on careful observation of celestial bodies like the sun and the moon, but also included other bodies like planets. The calendars were extremely important to all of the Mesoamerican civilizations. They were important in part because they allowed people to keep track of the seasons for agricultural purposes. However, they were also important for religious and symbolic purposes.
These are just a few of the many common characteristics of Mesoamerican civilizations.