The Mystery Cartoon Character Game, ongoing-ier.

A look at the list reveals we need this character to complete a duo...

1) I usually look on the bright side.
2) I am quite partial to cheese and crackers.
3) I am unaware how much I rely on my pet.

Oh, this must be Nick Park's peculiar inventor, Wallace, from the Wallace and Gromit series. Wallace is mighty partial to his Wensleydale cheese, going so far as to journey to the moon to get some. Yes, the moon is made of cheese, but not Wensleydale nor Stilton. Somewhere down the line, I'll have to find out the name of that cheese that's made in Sweden and is seen in almost every cartoon: deep yellow color, cut as a triangular wedge from a wheel, and dotted with holes.

Spot on, OUB - Wallace it is!

I always thought the cartoon cheese was the Swiss Emmental cheese - the similar Swedish cheese, Grevé, is usually paler. But I am no expert!

Splendid, thank you for that handy info, PeterHale. America tends to add annetto to cheese so it won't resemble soap. So Swiss Emmental and Swedish Grevé ... got it: the cheese of cartoon legend.

I hope this one's worthwhile:

1) This character appears only once in a theatrical cartoon short. It's a monochrome cartoon that's now in the public domain.

2) In-story, this character is never called by name; his name is only known from the title card, and then it really only names his breed.

3) This character isn't human. He's a quadruped, furry, and doesn't speak English. Knows how to get rid of a hobo, though.

I checked all the animated shorts in the public domain, and couldn't find any that match these clues.

I'm positive that this one's public domain, since it's on a compilation set of public domain cartoons, alongside many Popeye and Betty Boop cartoons, and that Pantry Panic one with Woody Woodpecker that Walter Lantz Studio let slip. Maybe I need to be more specific.

4) This character is a canine, a cute little doggie. Perfect pet for a little boy.

5) What's weird is that he's taken in by a family of cats: a mother cat and her son. In fairness, Mama Cat initially doesn't want "that filthy thing in my house." She changes her mind by the end of the cartoon.

6) In this cartoon, the natural enemy of dogs isn't cats, it's hoboes; especially one that practices home invasion and domestic terrorism.

I've looked high and low, and just can't find the right doggy.

I really hope these last clues do the trick. Somehow, I equate unguessed with unloved.

7) Debuted on Friday 23 August 1935.

8) Produced by Van Beuren Studio in New York.

9) This cartoon has nothing to do with a certain chief engineer securing a place aboard the Enterprise.

Ah... got it. It's Scotty, from Scotty Finds a Home. I've never seen this one.

Absolutely yes, this is Scotty, the valiant little Scottish terrier from the Van Beuren cartoon Scotty Finds A Home. Like all of Van Beuren's works, this cartoon is public domain, and can be found on various cartoon compilations. Scotty is never called by name in this cartoon; we know it's "Scotty" only from the title card. Much thanks, SaltyBoot, for saving Scotty from the forgotten heap. I'll add on your newest +1 while you take control of the board.

Believe it or not, this one is not on the list.

In my first short, I was not the star.
After my debut, I quickly became the star of many shorts.
I was paired up with an annoying little character.

Aha! The stuttering star of Looney Tunes, Porky Pig!

1. He wasn't the star of his first short.

2. However, he did go on to become one of Warner Bros' biggest animated stars.

3. At first, he was paired with Gabby Goat, who was quickly removed.

Th-th-th-that's all folks, if I'm right.

Yep, that is correct. Although in clue 3 I was referring to Daffy, since he annoyed Porky so much. But Gabby definitely works.

Thanks, Salty. Now here's another easy set of clues:

1. I wear a trademark derby.

2. I talk like I come from Brooklyn.

3. I often interact with one who'd rather be friendly, and also live up to my own name.

I remember tough-talking Spooky the Ghost from the renewed Casper The Friendly Ghost series. He began life in Harvey Comics, and proved popular enough to import into the animated cartoons.

Yes, OUB, Spooky it is. He actually first appeared in some of the old theatrical shorts, when Casper began to do more than just look for friends.
All clues are self-explanatory, so you go again. Good job.

Well, here's a surprise: we've tapped one half of a cartoon pair, but left the other half untouched. I shall correct this forthwith.

1) This character appears in a series of cartoons no longer in production.

2) Though he's the title character, his cartoons were embedded within another cartoon series headlined by a bigger character. But, hey, screen time is screen time.

3) Despite having a reasonably competent assistant, this character is woefully inadequate at his job, and too full of himself to realize it. One must wonder how he managed to attain his status, which is normally reserved for the most observant and analytical people in his field.

Aha! I know my Total Television characters quite well. This one is King Leonardo.

1. King Leonardo And His Short Subjects is no longer in production.

2. The series, like most other TTV cartoons, eventually became part of "The Underdog Show."

3. His assistant was Odie Colognie, but His Majesty wasn't a very good ruler.

I'm going to suggest it's another character...
Since I was the one to offer up Blabber Mouse, I think this may be his partner and superior, Super Snooper, from H-B's Snooper and Blabber series.

Yoy, do I feel horrible. Here, EmeraldIsle posits King Leonardo, who meets 90% of the clues' parameters. However, I have to point out that kings attain the throne either by being born in the right bed (birthright) or by slaughtering all opposition (conquest). I really can't name any kings that attained the throne by observation and analysis.

No, PeterHale's posit of Super Snooper comes much closer, since a detective relies on observation and analysis to solve mysteries. And Super Snooper meets all the other criteria as well; therefore, I must award PeterHale a rightful +1 for deducing a detective as the Mystery Character.