Uncanny X-Men Vol.1 #108
On the far side of the universe alone and cut off from their mentor, the X-Men must face their worst nightmares if they are going stop the mad Emperor D'Ken, from unleashing the unimaginable power of the M'Krann Crystal upon the universe.
Printed: Dec 1977
Writers: Chris Claremont
Art: John Byrne and Terry Austin
Cover: Dave Cockrum