The E.C.A.C., or Enormous Chemically Altered Cracker is used to nerf , the final target mob in the  quest.
Provided by Wrenix's Gizmotronic Apparatus during the quest Plundering the Plunderers.
Wrenix's Gizmotronic Apparatus is a mechanical vendor, and will supply as many E.C.A.Cs as you want while you are on the quest, but the item is unique, so you can only acquire one at a time. One should be enough to do the quest, but you can get a replacement if you need to.
Since Polly will no longer respawn for you once you complete the quest, the E.C.A.C. is nearly useless afterward (TBD if you can use it if you are assisting another rogue with the quest), and can be discarded.