...and that was true at Marvel Comics as well, as four of its greatest monster heroes, all of whom had their own series at the time, gathered in Marvel Premiere #28 (February, 1976) by Bill Mantlo and Frank Robbins to deal with the fact that "There's A Mountain on Sunset Boulevard!" and the menace of the Starseed!
This story showed perhaps who the real monsters were...but who are these four Marvelous monsters that gathered together?
...bio-chemist Dr. Ted Sallis was working to recreate the "Super-Soldier serum" which created Captain America, but A.I.M. (Advanced Idea Mechanics) tries to get the formula, but he escapes with it, injects himself with it and crashes in the Florida Everglades where the formula (and mystical energies of the area) transform him into the mindless monster...the Man-Thing.
...as well as vampire like traits including the need for blood and a more nocturnal lifestyle.
Werewolf By Night
Sadly, there was only one issue of this magazine (though all the characters in it continued on at Marvel...even meeting with some of the monsters mentioned above!).
While the Legion of Monsters isn't as well known as the Avengers, this team did make a mark all over the Marvel Universe including the Avengers!
You can even find the Marvel Premiere issue reprinted in Marvel: Legion of Monsters (2011), along with a few more recent stories (and stories from the Marvel magazine, Legion of Monsters!).