While Quicksilver and the Scarlet Witch are allowed to appear on screen as "Avengers," they're not allowed to be referred to as mutants, a term which is exclusive to the X-Men.

Scarlet Witch and Quicksilver are two of the most popular Avengers of all time. They also have a high profile, thanks to their appearances in the MCU and Fox X-Men movies. Now, Marvel Comics has ...