First of all, please keep in mind that there are currently very few ghosts available, as the game doesn't have many players yet. For each course, you can see a list of ghosts retrieved from the Nintendo Network. For the first track, I can currently see 11 ghosts (mine included) but there's no way to know if these are the best ghosts worldwide - there's no "top 10" option.

You can download any ghost from the list and keep up to 4 per track (max 16 ghosts total). You can watch the replay of any downloaded ghost with fixed camera. You can also see the ghost info from the menu, for lap times and vehicle parts.

Anyway, I still don't know how big the ghost list can be, or if the list presents a worldwide top or a relative number of ghosts slightly above or below your time. You can upload your ghost when you finish the race or later from the menu, with the option to add a miiverse post that will appear in the list.

As is Mario Kart tradition, players will be able to race against ghost data from friends, or even the top 10 worldwide racers. Players can try to beat them or just pick up a few tips and tricks from studying the best.

同日大阪市内で開いた2014年３月期の決算発表記者会見で、「マリオカートを遊んでいなくても、自分の順位や友達がどんな状態にあるのかが分かるウェブサー ビスを用意しようとしている。近いうちに詳しく出せると思う」と述べた。

It makes me very annoyed that they're likely recycling MK7's system of ghosts. I feel like if top 10s were in the game that Nintendo would have definitively told us that by now (Heck, they've told us everything else).