But didnt she first appear in double dash solely to be toads partner? besides there arent any other filler characters and waluigi isnt really a filler character anymore either, he appeared in MARIO DDR.
A filler character is basically a character created to be someone else's partner and to give players more otions when choosing a character. They typically lack originality. For example, Waluigi is just the "Luigi version" of Wario, who was created to be a tennis doubles partner. Toadette is the "female version" of Toad, and was created as race car partner.
This is what makes them filler character (based on the video games) and how filler they are. On a scale of 1 to 10, (10 being the most filler) this is how they are judged by my standards:
Daisy= Nintendo didn't want to use Peach as a damsel again. Pro: Developed a tomboyish attitude.
Filler Score- 6
Waluigi= Cons: Camelot invented this character as a partner for Wario in Mario Tennis 64. Pros: He has only appeared in sports games and starred in Dance Dance Remix. Developed a comical, yet sinister attitude. This brings his score close to Daisy.
Filler Score- 7
Luigi= Cons: Invented solely to be a recolor for Player 2, he is one of the most developed filler characters. Pros: He gradually became one of the more unique characters in the Marioverse, although physically he still looks like a filler of Mario. He starred in a couple of games and is whiny/scaredycat. He also looks up to Mario.
Filler Score- 3
Wario= Cons: Also invented because Nintendo felt like Mario needed a more stable and reusable rival/enemy. His appearance also makes him a doppelganger of Mario. Pros: He got his own series and even developed his own greedy personality. He has gone out on many adventures alone and like Luigi, physically still looks like a filler of Mario. His own series of games pulls him up even further than Luigi.
Filler Score- 2
Toadette= Cons: Invented just to be a sports partner (like many filler characters) of Toad. Pros: She helped Mario learn his abilities in PPYTD.
Filler Score- 8
Koopa Kid= Cons: Has no existance outside of the Mario Party Series and was invented because Camelot was confused to whom Bowsers main minions should be. It is a filler character of the koopalings. Hudson had to continue using Koopa Kids after their first appearance in Mario Party and were established as official main minions of Bowser. Hudson didn't use Koopas because they saw an eventual spot for them as NPCs or maybe a character. He is one the worst filler characters. Pro: None really
Filler Score- 10 (worst)
All these characters filler scores may be changed in the near future. To me, Luigi is the the most developed filler character.
luigi- 1 NO way can you call him a filler character anymore
Toadette- 5 Shes starting to kind of make herself her own character (besides I am a defender of all things that have to do with toad)
Waluigi-7 If wario started out as a filler character and this is a filler character for a filler character???? still he does have a personality of his own now
daisy- 9 She is almost the same as peach. She is said to be a tomboy, but ive never seen her act like one. (Anyone looks like a tomboy next to peach)
koopa kid- 8 give KK a break!!! everyone seems to hate him worse than they hate navi... hes kinda different from the koopalings.
This is all my personal opinion. I believe wario is the most developed, but luigi is a close second.