Squadron Supreme: When Strikes the Squadron Sinister

Note: This collection covers most of the appearances of both the villainous Squadron Sinister team (native to the Prime Marvel Universe, aka Earth-616) and the heroic Squadron Supreme (native to Earth-S, aka Earth-712), along with some solo appearances. The notable exception comes from the Squadron Sinister's Nighthawk, who later became a member of the Defenders. I included the Squadron-adjacent issues below, but otherwise his other appearances can be found in Defenders.

Let the Game Begin
Avengers #69
Avengers #70
Daredevil #62
Avengers #85
Avengers #86

Enter: Dr. Spectrum
Iron Man #63
Iron Man #64
Iron Man #65
Iron Man #66

Who Shall Inherit the Earth?
Defenders #13
Defenders #14
Giant-Size Defenders #4
Marvel Team-Up #33

The Serpent Crown
Avengers #141
Avengers #142
Avengers #143
Avengers #144
Avengers #147
Avengers #148
Avengers #149

Crisis on Twin Earths
Marvel Two-In-One #34
Marvel Two-In-One #41
Doctor Strange #29
Avengers Annual #8
Thor #280