Yeah, but it decreases. If you take a cubic meter of a 100 kg mass, spread it out over ten cubic meters, then you've decreased its density by a factor of 10. The mass is still the same, but the density is changed. I don't know why you keep bringing up Frieza being on the ground or in the ocean or whatever like this matters all that much. A planet is thousands of miles wide, do you think being somewhat underwater is going to increase energy density billions of times over? Just to do some more math for you, suppose Frieza's planet-destroying blast contains "10^36 J" and is "a cubic meter" in volume. The exact figures here are irrelevant (like I said before, explosions losing intensity over distance is true regardless of how strong you think Frieza is). As it expands to the size of the planet (rapidly, given that it's an explosion) this volume will increase to about 10^21 cubic meters, and will accordingly decrease the energy density by that same amount. What was once 10^36 J/m^3 is...