This item from the Kirby series is not new to Super Smash Bros. but has made a not-so-shockingly return in Ultimate.
When you "eat" it, the spice is so hot you literally start spitting out fire. Making it pretty easy to damage an opponent. It's helped me out many of time.
And if you're smart, if you see a fighter other than yourself use it, GET OUT OF THE WAY. Because it's not a fight you can win easily.