Complex sentence: The second "New Mutants" series, launched in 2003, featured a new group of teenage mutants; unlike the original New Mutants, they were part of a huge cast of students at the Xavier Institute.
Split into simpler sentences: The second "New Mutants" series, launched in 2003, featured a new group of teenage mutants. Unlike the original New Mutants, they were part of a huge cast of students at the Xavier Institute.