Just as the title, I was given a Faelora egg from combining all the Mermaid Set things? The seashells and such from the sudoku seashell contest. I'm not sure if it was announced that combining all those shells would give you a sylvestie with a Certified name, but that's what I got. I just can't remember what a certified name does? I'm sure there was a post I read about it, but I can;t find it.

I'm pretty sure it doesn't mean much besides being, well, a named creature, but I gotta admit, this one got stuck with a hilarious name:

https://www.sylestia.com/view/pets/?petid=8403184

Yeah, the certified names are just for show/fun.
As for the shells, it's a retired feature, as you used to be able to collect them.
This is the overview of when it was announced.

Interesting. But looking at the announcement, it's weird that you can only get the shells via the beach seeking thing (I got my nine shells from the login rewards). I haven't gotten a single shell from the beach. I suppose that's why I didn't remember what it did. Thank you!

You could've also gotten them from leaderboards & I wanna say the bosses?
Like I said though, they are retired/no loner obtainable, unless you buy it through the dia shop or via the login rewards like you've said.
& If I'm not mistaken, Sylestiopoly is in a way, a replacement for it, at least as an active collecting feature.