Complex sentence: Meggan's most formidable talent is her ability to instantly mimic the powers of other superhumans, in one case turning into fully empowered duplicates of Dazzler, Rogue, Colossus, Longshot, Storm, Wolverine, Rachel Summers, and Havok in rapid succession.
Split into simpler sentences: Meggan's most formidable talent is her ability to instantly mimic the powers of other superhumans. In one case turning into fully empowered duplicates of Dazzler, Rogue, Colossus, Longshot, Storm, Wolverine, Rachel Summers, and Havok in rapid succession.