"Onslaught" is a crossover event that spans 30+ issues and encompasses the majority of the Marvel line from August to September of 1996. In the aftermath, several series were cancelled including The Avengers (1963), Captain America (1968), Fantastic Four (1961), Iron Man (1968) and Thor (1966), only to be rebooted with new series in November of 1996 in the "Heroes Reborn" universe.
Listed below are issues either brandishing an "Onslaught: Phase" or "Onslaught: Impact" logo somewhere on the cover, or issues that have been reprinted/collected in their entirety within the "Complete Onslaught Epic" series of trade paperbacks. Left off of this list in particular are issues that contain only a single page referencing the Onslaught crossover event such as The Sensational Spider-Man (1996) #8 and The Avengers (1963) #400. All issues, including the single page issues "missing" from this list, can be located on their individual "Complete Onslaught Epic" trade paperback pages.