My hardest gaming achievement was probably my perfect Hector Hard Mode run on Fire Emblem 7. Perfect meaning no casualties, among other challenging requirements for turn limit and gold/weapon management.
If I don't include self-imposed challenges, hardest game on its own was probably Megaman 7. MM fans probably laugh, but ffs that final boss x.x
NNID: Zephyr25 / PSN: Zephyr--25 / Switch: SW-4450-3680-7334