Full Immersion [for what it's worth]

SpoilerShow

I know I know, E=MC^2 suggests it should be significantly easier to create mass than energy, but in a matter like that magic has a tendency to follow with what you intuitively "think" makes sense rather than what's scientifically true.

Actually, you have it right in the story. 3.75 potatoes would weigh about a kilogram, requiring 8.99x10¹⁹ Joules to produce out of energy, according to E=mc². The Tsar Bomba was 2.1x10¹⁷ J. This means half a kilogram of antimatter is a 21.5 gigaton bomb! *backs away slowly*