Here is a basic way to clone entities. Due to the way this system works, 1 command block is needed for each entity, including things such as the health of a mob. It would not be very practical to include all of these details when cloning entities, especially because the coordinates need to be set in each command block depending on the where you want point A and point B to be. This system is set up to only work with cows, pigs, sheep, rabbits, horses, villagers, and mooshrooms, but this system can be expanded to work with other entities. Due to the way this system works, relative coordinates for point B from point A are used.