Well. I decided to do some pointless math. XD I have good news for everyone who doesn't want to force feed their knuffels too.
Overall when you start looking at how much it takes to level up each level is about lvl*10 (then + 4-8points. But I like to simplify it down to lvl *10 Lvl 1 doesn't count because it's the odd ball out I've discovered.)
So overall we are looking at needing over 50000 points to reach lvl 100
So now lets break down about how many points we get a day. :3
Lets just assume a few things.
a.) Every day you feed your knuffel from 0 on both health and play to full.
b.) You play with your knuffel after every dig.
c.) Every dig skill you gain you put towards the knufflel's primary element.
d.) When you dig you never dig outside their element.
So. First calculation is how much you get from taking both happiness/food from 0-full.
The calculation is (98+(Level*2))/10
The reason it's /10 instead of /20 is because I simplified it. So I divided the bottom by 2 to calculate for both bars.
Next is the amount per win. We are just taking a mathematical average.
So we are looking at ((dig skill/100)*digs per day)*9)
Why *9? Because if we take the average of 6 points per win + 3 points for refilling happiness/food and the point for digging we get 9
For fails we are looking at
(1-(dig skill/100))*digs per day)*3
What does this mean overall? Well if you factor in all those numbers then divide it by the number of points you need per level you can figure out how many days it would take to level up your knuffel on average.
Heres the graph.
So without force feeding you are looking at leveling about every 5 days.
(yes I am a very silly nerd that likes math. XD)
If you noticed I stopped the graph at lvl 91. Thats because you won't be able to add any more points to a knuffel's own element after that level. So it' throws off my mathematical equation at that point. It goes back up a tiny bit and stays around 5.
(0) 
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Or maybe a prince?
I expected wings but not Pegasus.
