I don't think you should add "The Rooster" from the "If I Were the Letter B" song; he's just a rooster, nothing special. But you can add:
BESSIE THE GOAT--the goat that "maaa's" during the "B" song.
HENNY DRUMSCHTICK--a Muppet tribute to Rodney Dangerfield/Henny Youngman. Appears in an early season 25 episode and tells a "joke" about the creation of eggs. He's the rooster puppet with baggy eyes, a white collar, necktie, and brown feathers on the side of his head (a bit of a toupee).
ADRIEN BIP--a contestant on "What's Prairie's Problem?"; a green AM with curly black hair, small orange nose, and a brown business suit.
FENWICK LaTEUSSE--another contestant on "What's Prairie's Problem?"; a short lavendar AM, and has sleepy eyes, orange nose, glasses, slicked, parted hair, and a red plaid suit. He's a very nerdy and annoying character.
LUCY JONES--a version of Betty Lou from a 1969 game show, "Pick Your Pet".
SMILIN' JACK--owner of a hat shop. He's a lavendar live-hand AM with thinning brown hair, eyebrows, and moustache, pink nose, sunglasses, and a loud green-plaid jacket.
HEADLINE HOWIE--a lavendar live-hand AM with fuzzy brown hair and moustache, pink nose, beady eyes, round-rimmed sunglasses, red turtleneck, brown jacket, and grey hat. He appears in #796, and known for rhyming headlines.
SAMMY AND FRANKIE--two AM brothers who fight over an apple in a Super Grover sketch. Neither is identified as who's who. One is pink with tan hair and a red/black/green/purple striped shirt, and the other is orange with brown hair and a red/white striped shirt.
WILLY NILLIE--a pink AM boy with fuzzy orange hair that appears in another Super Grover sketch.
MAX--owner of Max's Barber Shop in the same sketch with Willy. He's a live-hand lavendar AM in a barber's uniform, with brown hair, moustache, sleepy eyes, and a pointy nose.
LITTLE JUDY FINSTERMACHER--a small orange AM girl with black pigtails in yet another "SG" sketch.
And here's a group of characters from "Here Is Your Life: Sneaker":
RIGHT SNEAKER--a red Converse sneaker. His mouth is the sole and his eyes are above the toe.
RITA RUCCI--designed Right Sneaker; a lavendar AM with frizzy orange hair, sleepy eyes, orange nose, large earrings and a leopard-print shirt.
GYRO SPINNIAPOLIS--made Right Sneaker; a fat blue AM with thinning brown hair, sleepy pink eyelids, pink nose, white (?) shirt, and red plaid vest.
LITTLE LIZZY HAMMERTOE--wore Sneaker; a pair of bare human legs wearing dark blue jeans. She's possibly played by Pam Arciero.
LEFT SNEAKER--Right's friend; looks like Right, but is painted gold and added with a bunch of junk as an art display.
P.S.: Who is "Howie", the one on your list?