All Just a Dream: The ending of "Run, Sheep, Run", "Bottles" and "Little Ol' Bosko in Bagdad". The first one explicitly makes it clear its a dream from the start, and the other two are more subtle about it.
Anti-Climax: The end of "The Old Pioneer"; during the battle between the indian tribe and pioneers, when the Indian Chief is just about to attack the eponymous pioneer, he finds out from the little indian kid that they saved his life beforehand, and at the drop of a hat, he changes his attitude and instantly calls off the battle. However, given it's a story told from the perspective of an old man to a kid, he may have just been embellishing.
Art Evolution: The early cartoons were basically just more polished versions of Harman-Ising's Warner Bros. cartoons (i.e. rubberlose limbs, circular, simplistic character designs with more design details and the obvious addition of color), but art studies and research allowed their cartoons to go in a more illustration like direction (comparing Bosko in "Parlor Pranks" and "Run Sheep Run" especially highlights this transition) and by the end of the series, they settled on a more streamlined, flexible drawing style not unlike what Disney was using, something that would transition into Harman-Isings later MGM Oneshot Cartoons.
Ironically, the two curious pups were drawn almost naturalistic in design in their initial appearance and both were identical to each other. Subsequent appearances made them much cuter looking, and gave them different color schemes.
As noted above, Bosko, after initially retaining his cartoon design in his first two appearances, abruptly gets a total design overhaul into an African American kid in "Run Sheep Run". His dog Bruno likewise got a redesign, looking like a gangly bloodhound as opposed to a rubberhose dog, and Bosko's girlfriend Honey likewise was overhauled into an African American child when she started appearing.
Ascended Extra: The unnamed protagonist mouse of the short "Alias St. Nick" would go on to star in two shorts of his own (one in this series, "Little Cheeser", and another ("Little Buck Cheeser") in the MGM Oneshot Cartoons, after this series folded).
Badass Baritone: The villain of "To Spring", Old Man Winter, has a very deep, booming voice.
Bears Are Bad News: The conflict of "Run, Sheep, Run". Initially it's just a Black Sheep playing "Boy Crying Wolf", and Bruno dressing up as a bear to play a trick on the sheep (which nearly gets him shot by Bosko)—but then a real bear shows up near the end and gives them chase. Fortunately, it turned out the whole thing was a dream.
Big Bad: "Old Man Winter" from "To Spring", a personified winter cloud whose is not only a jerk, but also has a very strong gale that is strong enough to revert the Dwarves attempts to bring Spring forward, and wreak havoc on their underground weather factory. With enough effort, he's defeated and Spring is restored, but he promises that he'll inevitably return.
Big Friendly Dog: As he was in the original Bosko shorts, Bruno is a large, friendly companion to Bosko.
The eponymous hound dog in "The Hound and the Rabbit" seems to be a threat to the little rabbit at first, but he soon turns out to be very friendly.
Bowdlerise: When it was aired on TV, "Toyland Broadcast" has a large chunk of its running time cut off to eliminate the lengthy ministrel show and sambo band sequences, which reduces the edited versions running time to 4 minutes.
Bratty Half-Pint: Wilbur the Cat from "Bosko's Parlor Pranks". He is an obnoxious little kid who incessantly wants an ice cream cone, and Bosko tries (and fails) to occupy him with stories of his previous adventures while Honey goes out to get him ice cream.
The Baby Bottles in "Bottles" are harmless, but quite whiny and annoying.
Little Cheeser is also kindof a brat, but is very na´ve, easily misled and only mildly stubborn in contrast.
Cats Are Mean: "The Discontented Canary", "When The Cat's Away", "Poor Little Me", "Little Cheeser" and "Alias St. Nick".
Wilbur the Cat from "Bosko's Parlor Pranks" is pretty precocious and impatient to Bosko too, but that's to be expected from a kid his age.
Chekhov's Gunman: In "To Spring", the Dwarf who was initially having trouble getting his pants on while the others worked turns out to be instrumental in helping the lead Dwarf push the giant lever of their factory (and was previously kept from doing this due to the raging stream he was stuck in), thus making the plants strong enough to stand up to Old Man's Winter gale, and thus forcing him to give up and fade away.
Christmas Episode: "Alias St. Nick" and "The Pups Christmas". "Toyland Broadcast" is presumably set during Christmastime, and it was formerly aired (albeit in heavily truncated form) every Christmas on Boomerang.
Cunning Like a Fox: The sneaky Fox villain in "The Hound and the Rabbit", who is trying to kidnap a group of playful rabbits.
Dark Reprise: For a brief bit during the climax of "The Lost Chick", the "We Told You So!" taunting song sung by the other squirrels is briefly recalled while they're starving in a winter storm, complete with a gnarly tree pointing it's branch at them like a finger.
Digital Destruction: Good quality restored prints exist of many of these shorts (both on the obscure Happy Harmonies laserdisc set, as well as airings on Cartoon Network) but "Hey Hey Fever" and "The Old Plantation" has some noticeable DVNR art-erasing in several parts of the cartoons. The boomerang airing of "The Discontented Canary" had some nasty DVNR inflicted on an already rough looking transfer.
Good Angel, Bad Angel: "Little Cheeser" has the eponymous mouse accompanied by these, and the Angel ultimately wins out in the end after the shoulder devil leads him into trouble a few times.
Grass Is Greener: The plot of "The Discontented Canary"; the canary simply wants to live out of the cage and fly free, and gets its wish, only to quickly find trouble outside with bad weather and a rather hungry cat, which quickly sends it flying back home.
My God, What Have I Done?: In "Run, Sheep, Run", Bosko has this reaction when he finds out the "Bear" he shot was actually Bruno in a costume playing a trick on his sheep. Fortunately, Bruno wasn't harmed and was just hamming it up, much to Bosko's irritation.
Our Ghosts Are Different: "Bottles" gives us the "Spirits of Ammonia" late in the short, a trio of three living Ammonia mists sent to capture the Shopkeeper.
Pain Powered Leap: The Bobcat in "Poor Little Me" is so repulsed by the skunks (and later his families) odor. that he's sent flying into the air screaming, and rolling around the ground in agony.
Shoo Out the Clowns: When the Poison Bottle puts his evil plan into motion during the climax of "Bottles" and has the witch send the Spirits of Ammonia to capture the shopkeeper, all the other living objects in the shop vanish, with the baby bottles even fleeing back into their box in terror.
Shout-Out: "Toyland Broadcast" is loaded with rerefences to famous radio stars of the time, including The Brox Sisters, Bing Crosby, the Mills Brothers, Kate Smith, the Boswell Sisters, Paul Whiteman, Rudy Vallee, Rubinoff and Ethel Waters.
In "Poor Little Me"; The bobcat's "I'll Be Glad When You're Dead, You Rascal You" ditty is a direct reference to the same song by Louis Armstrong.
"The Early Bird and the Worm" features two crows, who have personalities that are obviously based off of the then-famous radio stars Amos 'N Andy.
Both "Old Mill Pond" and "Swing Wedding" feature parodies of black musicians, including Cab Calloway.
Standard Snippet: in "Poor Little Me", When the Bobcat is burying his now stinky clothes, a snippet of Chopin's "Funeral March" plays.
Stock Animal Diet: The Fox in "The Hound and the Rabbit" attempts to kidnap and eat a group of rabbits that the hound had just befriended.
Stock Footage: "Bosko's Parlor Pranks" is basically nothing but recycled animation from the earlier Bosko cartoons, done by Harman And Ising in order to fulfill their yearly quota of shorts.
Footage of two French Dolls on a piano in "Toyland Broadcast" is recycled from an early Merrie Melodies short "It's Got Me Again!", complete with reusing the same "Apache Dance" music cue.
The first scene of the Mother Hen in "The Lost Chick" is partially recycled from a scene in the Merrie Melodies short "I Wish I Had Wings".
In "Run Sheep Run", the first scene of Bosko running from his house after Bruno (disguised as a bear) with his shotgun is partially recycled from a scene of Pan the Faun running (ironically, away from a pack of hunting dogs) in a previous Harmonies short "Tales of the Vienna Woods".
"Pipe Dreams" recycles a bit of the toy horse animation from "The Old Plantation", although the animation is redrawn to fit in the context of the cartoon.
Unintentional Period Piece: "Toyland Broadcast", due to it's abundance of Radio pop culture references, is basically a time capsule of 1930's pop culture.
Visual Pun: The menace of the worm in "The Early Bird and the Worm" is a baby rattlesnake—as in, a snake that carries a baby rattle.
Vocal Dissonance: Even before his redesign, Bosko had two very different sounding actors in his first two MGM appearances.
We Will Meet Again: Old Man Winter says something to this effect at the end of "To Spring", claiming that "(he'll) be back before you know" before he fades away for the time being. Given he's a personification of a season, this is a given.