Pandora is Lucy's rival. She was a normal girl before but she become part of a certain experience. Just like lucy, she can also use the Ketsueki tamashī no tsumi"Sin of the blood soul", abridging Ketanotsumi(the purple the tentacles that come from Lucy's back is the Ketanotsumi. The difference is Pandora's Ketanotsumi is green, while Lucy's is Purple). Lucy can use 3 Ketanotsumi while Pandora can use 6.
Ketsueki Tamashi no Tsumi or Ketanotsumi, is a ability of Lucy and Pandora of fusing their spiritual energy with their blood, allowing them to manipulate the energy-blood into forms of energy made tentacles or any other large sharp forms, usually from coming from their back.