In the end, the best option would be his ability to use electricity now. However, making an electric vehicle was beyond Billy's ability.
"Still… Who knows, if I managed to make a crossbow like that, maybe I could make a car that consumes mana to move," Billy thought.
That would require dozens of prototypes as well, and it would consume a lot more time since it would need more materials as well. Nevertheless, it would be a good time investment, and in the future, they would cut off the duration of the trips. Even cutting it in half would be nice.
Along the trip, Billy also tried to make some miniatures out of earth and steel, but they didn't have any effects. They didn't have any use… until now. His power mostly worked to make things work better, as weapons and as tools to make him sturdier or faster, but creating something with another purpose was new territory.