(6)Gilderoy Lockhart
(11)Percy Weasley
Two fantastically obnoxious characters, but I think Percy is just better executed. His letter to Ron in Book 5 just stands out way more than anything Lockhart has done.
(3)Lucius Malfoy
(14)Errol
Yeah...I've never been terribly endeared towards the pets.
(7)Phineas Nigellus Black
(10)Pomona Sprout
I just never got a strong feel for Sprout's character, honestly. Always so in the background.
(2)Nymphadora Tonks
(15)Marjorie Dursley
(mild SPOILERS I guess)
Marj needed a redemption scene at the end of book 7. The potential was there--obviously she had interest in Lilly's world, and Harry knew about her interest. All that needed to happen was a scene where Harry goes back and talks to her one last time. That's not the epilogue we got, unfortunately.
As such, I guess I'll vote for Tonks. She's not as well-explored as a character as I'd like, but does have a complete story arc, and random moments of badassery/likeableness.
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Cats land on their feet. Toast lands peanut butter side down. A cat with toast strapped to its back will hover above the ground in a state of quantum indecision