Hello ******!
Every 20% Nana Gains a level, except for the first 40%.
Here's a pic I found on Reddit.
Link to reddit post
https://www.reddit.com/r/SSBM/comments/34ba6b/my_friend_bigvegetabluntz_discovered_a_breakdown/
Interestingly there's a rumor you can make Nana act mote aggressive if you have an IC cpu in the slot you're going to play, make them level 9, and quit to the main menu, then start as a human. Unfortunately I think it's a placebo effect and every clip showing off Nana's improvement are at high percents, they were just looking for her to act more aggressive. Contrarily to what I think, people have stated Wobbles thinks it has some effect on Nana, like better DI.
You can find a ton more Nana tricks reading forums. (At the moment, I'm trying to finish reading the entire general chat) So if you're interested I'd recommend searching for forums with all the information, before creating one. Anyways, if you have any more questions feel free to ask!
-Vorporal