I'm not sure what you qualify as "normal". Darmanitan starts out in Standard Mode, and if it has the ability Zen Mode, it will transform from into Zen Mode once its HP falls below 50%. This means that a Darmanitan with the ability Sheer Force will not transform. Seeing as Zen Mode is Darmanitan's Hidden Ability, you will have to breed for it. Wild Darmanitan will never transform.