Premise[]
Certain epic level creatures are literally landscapes. Specifically, Genius Loci is described as anything from an underground lake, a large valley... or a small moon. Let's just get an estimate for the last one. I should note Genius Loci specifically can manipulate its body to attack enemies.
Calc[]
The smallest moon in this solar system is Deimos, a moon of Mars, which is only 7 miles in diameter.
U=(3GM^2)/5R, where...
G = Gravitational Constant
M = Mass (in kg)
R = Radius (in km)
Gravitational constant is 6.674 x 10^-11.
Radius is 5.63 km, since that's just 3.5 miles.
Volume of such a sphere would be 7.48e11 m^3, density of stone tends to be in the neighborhood of 2750 kg/m^3 (with some variation depending on type of stone), so our mass is 2.057e15 kg.
So!
3GM^2 = 3 * (6.674 x 10^-11) * 2.057e15^2 = 8.472e20
8.472e20 / (5 * 5.63) = 3.010e19 Joules, Island level. Damn shame. So instead, let's take average size of smaller moons, since... well, Genius is never said to be the smallest moon. Let's look at this.
Of the list above, the lower half ends with its largest moon being Ariel, of Uranus, standing at 1160 km diameter. The average size of this lower half is about 502 km in diameter. Let's just entertain this as a very possible high-end, a default statement of the average "small moon".
New volume is 6.62e16 m^3, new mass is 1.821e20 kg.
3GM^2 = 3 * (6.674 x 10^-11) * 1.821e20^2 = 6.639e30
6.639e30 / (5 * 502) = 2.645e27 Joules, Multi-Continent level. Niceu.
Tallies[]
Genius Loci is a Moon (Low-End): 7.19 Gigatons of TNT, Island level
Genius Loci is a Moon (High-End): 632.17 Petatons of TNT, Multi-Continent level