This one blew my mind as a kid, and sent me scrambling for a copies of Bulfinch, Hamilton and any other references on Norse or Greek mythology.
the 1977 Avengers/Marvel Two in One crossover annuals in which Jim Starlin wrapped up his original Warlock saga. Starlin hit his peak as writer and as artist with that one.
Ooohh, those were good. I'd forgotten about that wrap up.
Too bad Starlin thought it was so good too; he's been telling the same story over and over again ever since.
My favorite part of Marvel's early annuals were the extras after the main story. Encyclopedia like pages of Mole Man, Skrulls, Namor, Dr. Doom, etc., details of the Baxter Building, a special page on each of the heroes (with info like Mr. Fantastic can stretch a maximum of (I think) 75 yards on a good day. And of course the first Silver Surfer story, with the page of him making Quasimodo humanoid so popular they made a black light poster and a jigsaw puzzle of it. "Thus, you shall suffer no longer!" "I'm changing...changing!"