Game environments are not built with a ruler and some tape, they are built with imagination and an understanding of what is needed to make the game environment. If you take the time to learn about what you will need to do before you being the process, it will make for better results in less time with less work.
The Lord of the Flies, the Muscimancer has studied magics that summon, control and otherwise deal with flies. The Fly Mage is an unwholesome character, also likely to have magics of disease, rot and pestilence up his sleeves. After fighting through his swarms of flies and his loyal acolytes and slaves, the Muscimancer reveals his final power, transforming into a giant half man half fly hybrid. He can fly, acid vomit, as well as continue to use spells, wield weaponry and command his swarms.