| Issue | #21 |
| Published | September 2007 |
| Cover Price | 2.99 USD; 3.75 CAD |
| Pages | 44 |
| Editing | Andy Schmidt; Nick Lowe; Will Panzo (assistant) |
| Characters | Multiple Man [Jamie Madrox]; Isolationist [Josef Huber] |
| Genre | Superhero |
| Pencils | Pablo Raimondi (signed) |
| Inks | Pablo Raimondi (signed) |
| Colors | Brian Reber (signed) |
| Characters | X-Factor [Multiple Man [Jamie Madrox]; M [Monet St. Croix]; Layla Miller; Rictor [Julio Esteban Richter]; Siryn [Theresa Rourke Cassidy]; Strong Guy [Guido Carosella]; Rahne Sinclair [Wolfsbane]] |
| Genre | Superhero |
| Script | Peter David |
| Pencils | Pablo Raimondi (signed) |
| Inks | Pablo Raimondi (signed) |
| Colors | Brian Reber (signed) |
| Letters | typeset |
| Notes | Recap of story-to-date and creator credits. Pinup is from cover to X-FACTOR #17. |
| Characters | X-Factor [Multiple Man [Jamie Madrox]; Rahne Sinclair [Wolfsbane]; M [Monet St. Croix]; Layla Miller; Rictor [Julio Esteban Richter]; Theresa Rourke Cassidy [Siryn]; Strong Guy [Guido Carosella]; Rahne Sinclair [Wolfsbane]]; Nicole; Val Cooper; Mr. Tyler; Mrs. Tyler; VILLAIN: Isolationist [Josef Huber] |
| Synopsis | In a castle of ice in a far off land, a fearsome being called the Isolationist sits and waits and plans...except he need wait no longer. He is coming to Mutant Town, and is seeking out Jamie Madrox. But whether he and X-Factor will be enemies or allies pales in comparison to the shocking developments involving Guido's new job offer, Rictor's unexpected call to action, Siryn and Monet's new case, and--most stunning of all--Layla's disturbing discovery of something even she didn't know. [per solicitation] |
| Genre | Superhero |
| Script | Peter David |
| Pencils | Pablo Raimondi |
| Inks | Pablo Raimondi |
| Colors | Brian Reber |
| Letters | Cory Petit of Virtual Calligraphy [as VC's Cory Petit] |
| Genre | Superhero |
| Letters | typeset |
| Notes | Recap of ENDANGERED SPECIES story-to-date. |
| Characters | Beast [Henry McCoy]; High Evolutionary [Professor Wyndham]; Snow Queen |
| Synopsis | Beast travels to see the High Evolutionary. |
| Genre | Superhero |
| Script | Mike Carey |
| Pencils | Mark Bagley |
| Inks | Andrew Hennessy |
| Colors | Raul Trevino |
| Letters | Joe Caramagna of Virtual Calligraphy [as VC's Joe Caramagna] |