| Issue | #27 |
| Published | December 1966 |
| Cover Price | 0.12 |
| Pages | 36 |
| Editing | Stan Lee |
| Notes | Disputed penciler credit--Werner Roth alone per Steve Whitaker, Nick Caputo, Carl Gafford, and Michael Evans; Werner Roth and Jack Kirby together per the original indexer. |
| Characters | The X-Men (Beast, Marvel Girl, Iceman, Cyclops); Mimic |
| Genre | superhero |
| Pencils | Werner Roth |
| Inks | Dick Ayers |
| Notes | Disputed penciler credit--Werner Roth alone per Steve Whitaker, Nick Caputo, Carl Gafford, and Michael Evans; Werner Roth and Jack Kirby together per the original indexer. |
| Characters | F: X-Men (Professor X, The Beast, Iceman, Cyclops, Marvel Girl, Angel); GS: Mimic (joins the X-Men), Quicksilver, Scarlet Witch, Spider-Man; V: Puppet Master, Defender (I; an android); GA: Ted Roberts, Zelda; Cameo Flasback: Fantastic Four (Mr. Fantastic, Invisible Girl, Human Torch, Thing) |
| Genre | superhero |
| Script | Roy Thomas |
| Pencils | Werner Roth |
| Inks | Dick Ayers |
| Letters | Sam Rosen |
| Reprinted | in X-Men (Marvel, 1963 series) #75; in Giant-Size X-Men (Marvel, 2005 series) #3 [1 page]; in Marvel Special (Marvel Italia, 1994 series) #12 |