Lunaris is able to quickly recover from Donald's barrage, and shows an impressive amount of durability. Given that he had prior used himself as a test subject for his prototype spaceship, it likely significantly strengthened him (even beyond the Moonlanders average strength being significant compared to the people of Earth).
It was pointed out in a previous Fridge that Della's rebuilt Spear of Selene, made with gold, should've burned up in the Earth atmosphere on re-entry. This likely explains why Lunaris' prototypes also tended to be unsafe, until he had her designs and some idea of what to build from other than gold.
Unlike Della, Donald moves and walks normally while he's on the Moon, with no given explanation.
The more likely explanation is that Donald was always just better at it, and that sailor outfit of his isn't just for show.
The less likely explanation is that the Moonlanders have increased the local gravity somehow, in preparation for the Earth invasion.
The impossible explanation is that Donald's combination of catastrophically bad luck and temper means he... can just ignore local gravity conditions under certain circumstances?
