Tingle for sure. I feel like I'm becoming that guy who wants to **** Yoshi in the main thread for Tingle because he's all I ever post about, but seriously his spinoff games are great and he would be an incredibly fun and unique character. I also feel like a key aspect, maybe the key aspect of the Zelda series is its zany side, and its strange NPCs, and I can't think of a better character to represent that side of the series than Tingle.
I really feel like that's a big part of what makes Zelda special. I've loved this series since I was five years old (that's a looong time) and what drew me to it was never the "coolness" but the mystery and the absurdity and all the weird wonderful color that separates it from so many other fantasy rpg series. Midna and Ghirahim and Vaati and Impa are all cool characters, but I feel like they could slot pretty easily into any Final Fantasy or Fire Emblem or Xenoblade game. No disrespect to those series, but there's just a particular spice that makes Hyrule Hyrule for me and it lies in the contrast between its darker high fantasy stuff and all the silly weirdness. Everything just has such personality and charm and nothing takes itself too seriously. There's an evil devil worshipping ninja cult, and their one weakness... is that they're obsessed with bananas. You can only win the respect of the proud mountain golems... by making their chieftain GET DOWN to a jaunty flute song. A highly advanced race of precursors has watched over the land for centuries from their palace in the sky... and they're just chickens with human faces.
THAT'S what Zelda is to me. And I feel like, with the possible exception of Toon Link, none of that really comes through in Smash. We just have the elfin hero (x3), the evil warlock, the princess, and the badass mentor ninja. And sure, we could add any number of other badass characters, but is that really what the series is about? At its core, Zelda is and always has been a deeply silly series. I just feel like there's always been this contingent of Zelda fans, like the people who were upset about Wind Waker's art direction, who want this series to be SERIOUS FANTASY WITH DEEP LORE, and no disrespect, but it's not. I's playful and wacky and it puts fun above everything else. Zelda is the series where attacking a chicken will cause an apocalyptic storm of chickens to come and attack you. Zelda is a series full of characters like Tingle and dozens of other lovable weirdos going all the way back to the "ITS A SECRET TO EVERYONE" guy. AND DAMN IT, WHO WILL SPEAK FOR THE WEIRDOS?
I know this is the Skull Kid thread, and I'm on board for Skull Kid, but that's because Majora's Mask is the Zelda with the most of the spice I'm talking about.