Polaris has a latent secondary mutation that allows her to absorb negative emotional energy to transform into a virtual powerhouse, with increased size, strength, endurance, and invulnerability. Her power also released the negativity back into her environment at an enhanced level, which caused others to act more violent, selfish, bloodthirsty, etc.
Lorna assumed the name "Magnetrix" in X-Men: The Hidden Years #3, but quickly dropped it. She was possessed by Malice from Uncanny X-Men (1st series) #219-250.
Lorna lost her X-Gene on M-Day. Apocalypse made her into Pestilence V in X-Men (2nd series) #182, and restored her magnetic powers. As Pestilence, Lorna had the power to assimilate hazardous materials such as poisons, disease, viruses, and bacteria into her cells, cultivate these pathogens, and release them to assail her victims at will. Apocalypse used nano-molecular machines to artificially recreate her powers as Polaris. As of X-Men Legacy #259, Lorna explicitly tests postive for the X-Gene again, meaning Apocalypse not only recreated her powers, he recreated her mutant genes as well.
Pestilence I belonged to a set of Horsemen that battled the Fantastic Four, and II battled Alpha Flight.