The easiest way is to play a Teeming Darkness card on Floor XIII and make sure that the last enemy you kill is a Neo Shadow. This may take a few tries, but it's how me and some friends of mine got it.
| Identifier (URI) | Rank |
|---|---|
| dbkwik:resource/670mPhTjb5R8Be_YgfTokA== | 5.88129e-14 |