X-666 was created by Blackheart by using his H'elian's Mirror Cauldron which creates inverted reflections of whomever stands before it. As X-23's antithesis, she appears to be everything Laura is not. Being a remorseless killer on the inside but a pure, blonde, all-American girl on the outside allows her to be "nuanced", having two layers.
X-666 was created by Rick Remender and artist Tony Moore and debuted in Venom's Circle of Four miniseries.
Major Story Arcs
Circle of Four
For further information: Venom
X-666 appears as part of Blackheart's answer to X-23 during his attempted take over of Earth. X-666 briefly takes on X-23, explaining how she's better than Laura because of her ability to hide who she truly is. After a short battle X-666 lets X-23 head off in search of Blackheart. X-666 continues to taunt X-23 along her way towards Blackheart, reminding her that her healing factor will not work in Hell. She allows Laura to continue as it will ultimately prolong her torment since she will not succeed. X-666 also tells Laura that Hell is where she belongs. Blackheart calls X-666 to convince the Ghost Rider to take his deal. Red Hulk jumps in and crushes X-666 with Venom on his back.
Powers & Abilities
X-666 seems to have similar physical abilities as X-23 but with no claws. She is armed with 2 metallic, razor sharp pom-poms.