1.) Ambush Bug. I just like him, at least when handled by Keith Giffen.

2.) Yes, some characters are inherently B-characters, in that they will never appeal to a mainstream audience, but they can still be a great chatacter.

Metamorpho- His original series had charm, imagination, and verve, qualities he's capable of bringing to any series he becomes a part of. His appearances in Brave and the Bold were favorites of mine and his role in the Defenders/Champions-like Batman and the Outsiders gave the series a lot of credibility as an organic development in the course of events in the DC Universe. 

E-Man- The OTHER shape-changing E-Man, who was a Charlton comics headliner back in his day, and a solid hope for success at First Comics, but his two-time status as a top tier character at a second tier company was never going to bring him lasting fame. 

As for villains with a low recognition factor, I like the Top. He died and more or less stayed dead for a long time. That has to be some kind of a super-power all by itself. 

And I like Marvel's White Rabbit, who was a sort of Harley Quinn before Harley herself. Absent the abusive boyfriend theme, however, and debuting against Spidey and the Fabulous Frog-Man, well, it was an inauspicious start to say the least. Now, any attempt to give her the spotlight is just going to make her look derivative, but she did come first.

In general, there are a number of characters whose light touch and sense of humor make them favorites of mine, but also keep them from finding a place in the hearts of those who like their comic fare more merciless and violent; more continuity-minded and "real."

As for whether second-tier characters can ever transcend their origins and find greater success later, well, never say never. Rocket Raccoon and Groot are much more merchandised and embedded in the hearts and minds of America than one could reasonably have suspected prior to their film success. The Vision seems to be finding fans he had no reason to have before. And of course, there's that scrappy little Canadian secret agent who went from a Hulk bit player to a face in the crowd of a team book that likely shouldn't have succeeded nearly as well as it did. He's top tier now. 

And again, stayed dead for the most part... White Lantern folderol notwithstanding. Talk about eliminating the intrinsic elements that make a character work. "Let's make Deadman... not dead!" A move dumber than the dirt he was buried under...

And I'd like to add that many of his most recent series have demonstrated a startling lack of insight or real-world knowledge into what makes the character work. How he could have been done so well for so long by so many and later fallen into the hands of such clueless, tone-deaf creators is a mystery... 

The new Neal Adams series is a nice turnaround in quality, however! Let's hope Adams is able to remind everyone of why this character is a classic and that the lessons stick.

Iron Man pretty much fills that position in the MCU...even being the character that finally brought Spider-Man into the fold. "He must be a Marvel character, he's hanging out with Iron Man!" 

It's amazed me what Marvel Studios has done with characters I would put as "C-listers" or below: Black Panther, Black Widow, Ant-Man, Guardians of the Galaxy...some of these were deep comic-readers-only people...now household names. 

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Totally agree with this, and I was going to mention Groot in my post, but could Rocket or Groot carry a film or an ongoing comic book series with them solely as the lead? That to me is A list and I think the answer is no.

So, yes, absolutely they are very popular in a certain way -- my nephew loves Baby Groot -- but I wouldn't personally classify them as having made the A list.

I suppose this may simply come down to what our definition of A-list is. Brian Rhodes mentions above that he would say Iron Man was B-list prior to 2008 because civilians weren't familiar with him. But I would say Iron Man has always been A-list because he has carried a solo book for decades and decades. Civilians are more likely to recognise Mr Freeze than Galactus... but it does not elevate Mr Freeze in any way above Galactus. Galactus is A-list. Mr Freeze is B at best.

At no point are these characters not deserving of their own titles; they just didn't have 'em. And I firmly believe that no creator develops a character to be second rate. I feel that every one of them wants to be the next Jerry and Joe, or Stan and Jack.

Incidentally, I don't think being cancelled (or nearly so) qualifies a character as a b-lister. At one time or another, that list included Batman, Wonder Woman, Green Lantern, the Atom, Hawkman, Daredevil, the Hulk, Iron Man, Iron Fist, etc.

My favorite b-list character is likely Captain Marvel Jr. Perhaps he wasn't in the day, granted, but I think he fell into that list when "Shazam!" came back out in the early 70s. As someone once noted... likely serious enough to be a JLA'er, a Titan, or a Legionnaire.

And, yes, I believe some characters are inherently b-listers given their respective powers.