The Mutant Massacre from October to December 1986 was one of the early crossover events that tied together the x-teams: X-Men, X-Factor and New Mutants. The comic list comes from the Wikipedia article, but this perfected order comes from ComicBookRealm.com and this forum post.
Uncanny X-Men #210 (Prologue)
Power Pack #27 - Not available on Marvel Unlimited
Daredevil (vol. 1) #238 is an unofficial crossover issue set after the events of the Mutant Massacre. The issue features Daredevil fighting Sabretooth after his escape from the X-Mansion.
This was originally Chris Claremont’s idea and he had planned it for a run solely in the pages of Uncanny X-Men. You can pick up the collected editions on Amazon in paperback or hardcover and I highly recommend X-Men: The Fall of the Mutants that came in 1988. A great sequel of sorts to the theme.
Until next time,