Deadpool #3 1994

Deadpool #3 (Marvel, 1997) finds Wade Wilson's healing factor failing, prompting him to seek out Siryn. Their pursuit of Black Tom Cassidy leads them to Doctor Killebrew, who reveals Deadpool is dying as his body rapidly consumes itself. This issue is notable for further exploring Deadpool's origin and establishing the critical vulnerability of his regenerative abilities, a key element in his character development during Joe Kelly's influential run.