They're not playing in an orchestra, but they're still pretty darned cute. I'll take these guys over the X-Babies any day, and a crossover wouldn't be unwelcome either. I'm still not sure about the long haired non-monster, but maybe the wolf insignia on his belt will be a clue for someone. Or the fact that he's on a dinosaur. Or the fact that it's now clear that he's not wearing a shirt under that harness thing. Update: It's Gullivar Jones, Warrior of Mars. See the comments.

They unhelpfully put a dozen other characters' names at the top of the ad. Note that he's lost one of his bracelets.

From Richard Arndt's site (and probably also listed in his book Horror Comics in Black and White: A History and Catalog, 1964-2004):
"Marvel Magazines Ad [Alfredo Alcala] 1p [Frankenstein’s Monster, Werewolf By Night,
Conan, Simon Garth the Zombie, Dracula, Gulliver (sic) Jones & Satana are featured in a l’il kids style illo.]" So that may be Gullivar Jones, Warrior of Mars.

http://www.enjolrasworld.com/Richard%20Arndt/Marvel%20B&W%20Horror%20Magazines.htm

And there's the wolf belt. Thanks Shar! I see that Gullivar Jones ran mainly in the color comic Creatures on the Loose, but he had stories in two issues of Monsters Unleashed.

I agree with Shar, it is Gullivar Jones. The wolf insignia on the belt is the giveaway along with the reptile he rides. Gullivar Jones was the "warrior of mars" and actually predates Edgar Rice Burrough's John Carter of Mars. I believe he was in the public domain, and Marvel printed some color books with him in it as well.

Here is a link where you can find the shirt. You'll need to scroll down until you hit the Monsters Unleashed issue.

http://marveluniversity.blogspot.com/2014/06/february-1974-part-two-once-hero-for.html