Recently, Gonzalo "ZeRo" Barrios has been playing quite a lot of Lucina, both at locals and even at a few bigger tournaments in order to test the waters with his newfound secondary.
Perhaps more surprising than how much success this Lucina has seen is the fact that Lucina appears to be the perfect secondary for ZeRo, not simply a good one.
The world's best Smash Wii U player recently put out this video explaining why he prefers to play Lucina instead of Marth. The reason is simple: Lucina has no tipper hitboxes.
Without the volatility of tipper hitboxes, ZeRo can simply rely on his ability to calmly space around and break down his opponents while playing instead of looking for minuscule sections of the sword that are stronger than others.
More importantly, Lucina actually helped him win DreamHack Austin. For several reasons, ZeRo struggles quite a lot against Mario, especially when it's Elliot "Ally" Carroza playing the Mario.
When they met for the second time that tournament, though, ZeRo broke out the Lucina for Ally instead of playing his signature Diddy Kong. Though the games were closer than ZeRo probably would have preferred, the Lucina pick got him into grand finals.
ZeRo's play focuses very heavily on his spacing. It's not too common that he hits somebody with a Diddy down tilt at point blank range. He always hits it from nearly max distance to be safe.
So when he grabs Lucina, a character who can wall people out and has an emphasis on her spacing, it just clicks for him.
Image courtesy of IGN