@HauntedPizza yeah i did think about that, but he could just have show a metal object being transform to rush or something like that before and dunno when the combat is in a room full of iron cage
the author did chose to introduce the Dwarven Iron Sand with the ground
yeah you would have a hard time introducing something like that well if you don't change anything but it would have been easy to change something, i think little details make great stories
or just maybe make the action a little more clear and focus on this weird new thing, and after having show it more that one case you make the MC ask what the fuck was that, but the author did chose to make one case and a dialogue END even if he talk more after he already kinda kill my curiosity with that
Edit : and well how to say i am just someone that read a lot of manga and i did only think about this for 2 minutes, i am sure someone who work in a job all about drawing and telling stories can figure something way better