To make the changes take effect, do I need to download the file from the header? Which exe file?
Maybe it would be better to make it similar to Letos's passive ability? Otherwise, it seems too straightforward. The difference could be that Letos's passive ability randomly selects a unit, while this ability can attack random cells. And perhaps some dependence on characteristics is needed, because the armies differ in both quantity and characteristics, and the catapult is always one, and simply mowing down 10% seems strange.
Currently, the catapult works mainly against low-level, numerous troops, and for high-level troops, the rounding goes to 0.