Not strictly as per OP but making Butters more than a nondescript background character worked out brilliantly.
Yamato and Sai amounted to nothing in Naruto.
Sai's was worth it just for the moment near the end of the war when everybody's having a designated "awesome moment" and he leaps into the fray yelling "I'm a member of Team 7, too!" only to be swatted out of the air like a fly and left bleeding on the ground. End scene.
That's not even a joke or a comedic reduction. It seemed like the author was just torturing the character in a nod to the fanbase.
Toph is a great pick.
Beerus made me stop watching Super, though.
My pick for "Worst" would be basically every non-antagonist character added after the Soul Society Arc of Bleach. There were already too many characters with not enough being done with them, and none of the further supporting cast additions had sufficient value to make up for the fact they were cluttering up the place.
Death Note
Misa, Near, Mellow.
Just why.
Lucky made me stop watching King of the Hell. Freaking hate him and he ruined Luann too.
Even the music hates him.
And of course, the original Poochie:
Scrappy Doo
Can't believe nobody mentioned cousin Oliver from the Brady bunch. You guys know what that is right? Please?
/Old man
Oliver was terrible.
As much as I hate Scrappy, I always found Scooby Dum far more intolerable
Brady bunch manga...Best and Worst additions to an existing cast in animated media?
Mari is a key component in Anno's mind games with the Evangelion fanbase.
When he created Evangelion he created characters with deep flaws who were essentially broken people. The otaku, however, fetishized the girls of Eva to a degree he hadn't anticipated or wanted, which upset him, because they didn't get the point of his story. (Of course, Gainax was more than happy to sell the merch.)
Rebuild 2.0 was written to give the fanbase "everything they wanted" (and 3.0 to take it all away), so Mari was intentionally developed to be waifu bait. That's why she adds virtually nothing. She has no purpose other than to appeal to otaku.
Von Stroheim from Jojo's Bizarre Adventure Battle Tendency.
As much as I hate Scrappy, I always found Scooby Dum far more intolerable
I second these answers, though I'm of the opinion that Glim Glam is pretty awesome.My Little Pony: Friendship is Magic added essentially a seventh main pony character with Starlight Glimmer, who has had pretty consistently great focus episodes, but the character herself is still love-her-or-hate-her. So instead I'll focus on another character added to the supporting cast: the Great and Powerful Trixie. Trixie is a wandering stage magician who pretends to be a powerful wizard, boasting of her skills and making a show of everything. The type that refers to herself in third person. She was actually introduced back in season 1 for one episode and was popular then, leading to her returning for an episode in season 3, but they clearly struggled on how to make her work as a recurring character, leading to her third appearance not being until season 6 (minus Equestria Girls). But after that episode, she pretty quickly became a major recurring character.
In truth, though she was popular among fans, I didn't particularly like her much. She was kind of amusing, but there wasn't much to her character. Fans often portrayed her as a Vegeta-style rival to the main character, Twilight Sparkle, which is what her season 3 appearance went with, having her come back with an evil amulet to boost her power and fight her, but it just didn't work. However, when she came back in season 6, they paired her up with Starlight as hergirlfriendBEST FRIEND, and everything clicked. With both being former villains, Trixie could connect with her and thus could drop her guard, leading to great interactions and surprisingly natural dialogue between the two. She has also become more of a goofy character, which has done wonders for her.
These guys
I dunno if you're talking about best or worst, but they were in the same, singular movie.
My vote:
Ogiue from Genshiken
Your vote for what? Best or worst?
What a half-assed post.
These guys
My vote goes to Neo.Have RWBY on my mind so for best I say Qrow.
While he's mentioned a few times in Volumes 1+2 it's only in Volume 3 where he officially joins the cast and we find out he's a perpetually drunk troll of a mentor.
Beerus is the best DB character aside from Evil Vegeta and Kid Goku.
Conversely, pushing Tweek into the spotlight after Kenny "died" was a huge flop.Not strictly as per OP but making Butters more than a nondescript background character worked out brilliantly.
Best:
Janna from Star vs the forces of evil
Upgrading her from a minor side character in season 1 to a full fledged supporting character in season 2 is one of the best decisions the show runners have made.
My vote:
Ogiue from Genshiken
Best:
Janna from Star vs the forces of evil
Upgrading her from a minor side character in season 1 to a full fledged supporting character in season 2 is one of the best decisions the show runners have made.