In the grand magic games arc we saw several team events that use a lot of magic events. Which are "Hidden", "Chariot", "Pandemonium", "Naval Battle" and "Battle Royale" etc.
In the world of magic, we see magic circles being used to create these events. For Example, creating the water sphere in Naval Battle or Peripheral Chariots. These may be comparatively easy, however it would require lots of magic power to create thousands of exact clones (Hidden) or 100 monsters of Pandemonium.
So who/which guild/how was used to create these events since they would require an absurd amount of power.
Considering, How powerful would the user be if he can create a monster which can fight on level footing as an S-Class mage? Thousands of clone which may have same power as that of user(?)