Complex sentence: The creatures were invented by then 3rd Grader Arthur Kay, a current high school student, his classmate Carlie Robbins then coined the creatures "zenzizenzizenzics" for a weekly assignment in which a word was researched and redefined.
Split into simpler sentences: The creatures were invented by then 3rd Grader Arthur Kay, a current high school student. His classmate Carlie Robbins then coined the creatures "zenzizenzizenzics" for a weekly assignment in which a word was researched and redefined.