So, Wattpad's search function is your first and worst enemy, but that's also where the hunt gets interesting. I've been trawling the Kirby tag for years, and the main thing to understand is that new stories with original characters don't always get tagged perfectly. You have to get creative with your searches. Try combinations like 'Kirby OC', 'Dream Land OC', 'Kirby x OC', or even character-specific tags like 'Meta Knight OC' or 'Bandana Dee OC'. A lot of writers are shy about using the main 'Kirby' tag if their story is heavily OC-focused, thinking it won't fit.
I'd also strongly recommend diving into the profiles of authors who have one story you like. Often, they'll have other WIPs or older stories that didn't gain as much traction. The community aspect is huge here—leaving a comment or adding a story to your reading list can sometimes alert the author that there's interest, and they might mention other similar works in the fandom. It's a bit of a network effect.
Don't sleep on the 'Fanfiction' category filter either. While Wattpad is flooded with romance, filtering by 'Fanfiction' and then searching within that can weed out a lot of the unrelated original fiction. Sorting by 'New' is obviously key for fresh content, but be prepared to sift through a lot of abandoned works or very short one-shots. The real gems are the ongoing series that update weekly; following the author gives you update notifications directly. I found my current favorite, a long-form adventure about a Waddle Dee mage, exactly that way—it had like twelve reads when I first clicked.