Okay this is my 50 cent.
Spoiler

Take Yuugi Hoshiguma. She is an Oni, probably the strongest Oni in Gensokyo.
Take Suika Ibuki, another candidate for the strongest Oni in Gensokyo.
Suika Ibuki claims that she can hold Youkai Mountain by herself.
How tall is the Youkai Mountain?
The highest possible altitude for sustainable life is around 20,000 ft. However, Youkai Mountain is based off of Lake Suwa, a real life Japanese lake that is elevated about 3000 ft up in the air.
So 3000 ft mountain. Sounds very underwhelming, right?
Well let's consider the weight of it.
Assuming that the mountain is simple conic figure, the formula for finding the volume is 1/3πr^2h.
Since h is 3000 ft = 1000 m, and that r is half of that amount, (500 m) the volume of Youkai Mountain is 261,799,387.8 m^3.
Assuming that the mountain is mostly made out of granite, the mountain's weight is 261,799,387.8 m^3 * 2.8 g/cm^3 * 1 cm^3/1.0 e-6 m^3
= 7.3304 * 10^11 kg.
Yeah.
If Suika can hold it, Yukari surely can, right?
...except she cannot.
Yukari is an unknown-category Youkai, while Suika is an Oni. Oni demons are known to be the strongest class of Youkais. So we can assume that Yukari's limit is about one-tenth of that, which is still a whopping 72,146,142 tons.
This math is probably very incorrect but it's what I got.