DNA Splicer
From TPPC Wiki
What it does: Allows Kyurem to fuse with Reshiram or Zekrom to obtain Black/White Kyurem.
How to use: Defeat N's Castle with Kyurem in Slot 1, and Reshiram or Zekrom in Slot 2. Attatch DNA Splicer to Kyurem.
How to get it: Defeating N's Castle with Kyurem in Slot 1. 10% chance of getting DNA Splicer.