To get Nona to lvl 20 doesn't take that long to be honest. You can do it in less than 1 hour on the first corridor! Should take about 30min max and can be done faster depending on how you play...
After beating the first enemy you get your first lvl up at the first bed. The corridor after the bed is your best XP farm!
The enemies will spawn all the time and you only need to kill 1-2 at the beginning to reach another lvl up.
Using your skill balls all for POWER lets you kill the enemies with 2 hits at some point till it reaches a single hit.
The spawning enemies will give you small XP after reaching a certain lvl but this is the point where the immortal enemy at the end of the corridor will help you out. (Guy near wooden horse)
By defeating him you can fill your XP bar up to the half or even more and he will regenerate his health really fast so you can knock him out over and over again.
The starting area is also the best option because after the futa village your skill balls will become useless! At the starting area you will even get skill balls till you reach max lvl which can be used to increase stats to your liking via the minigame. If you have patience you can make your skill balls multiply by hitting the 1~2 spot and reach even higher stats without using any cheats at all.
Why is the minigame removed later in the game?
My guess is that the player can use the minigame as some kind of exploit. If the max lvl wouldn't be capped at 20 but at 99 we still could increase our stats more and more up to the point where all enemies could be killed with a single hit!
This would also go for the bosses... Yet there will still be some players who aren't maxed or have lower stats but they can still be able to beat the enemies at higher stages even with lower stats. Imagine having to be lvl 60 in order to kill the tiger girl with atleast 50 hits when you are only lvl 15...
At the moment it's still possible to beat every stage even with a lower lvl. When I did my first playthrough I wasn't maxed out and didn't even use all skill balls. My lvl was 13-14 and the only problem I had was the tiger girl. It took me a few tries to beat her but in the end I made it even with low lvl.
Then after doing another playthrough with max lvl it was a piece of cake and all enemies no longer felt like a threat.
If all skill balls get put into
POWER the player can get 210-220 max
POWER! Depends a bit on the starting stats since you always start with random stats by starting a new game.
The
SPEED stat will make Nona freeze if it reaches 180, so a max stat of 179 for
SPEED is the highest a player should get!
I made a complete list of saves back then:
Without Cheats (Not up to date; Torture Room not completed!)
With Cheats
Cheat Engine Table
Cheers