12 Days of Pandora

Description
"Kill 25 enemies with shock weapons"

Guide
You must kill 12 or so people with every weapon type in the game, and a few other misc. kills like killing 2 people with the various elemental attacks. You can check this by going to the quests portion in the back menu, and press Y once. Should be the first one on the list.

Trivia
Could be a reference to "12 days of Christmas"