Single vulnerable vein or nail as life source

Talos

Talos's singular vein, running from neck to ankle and stoppered by a single nail, contained the ichor that gave him life - a detail that highlights both his vulnerability and the intricate design of his creation.

Pontianak

a nail (paku) driven into the hole in the back of her neck or skull renders her passive and able to pass as an ordinary woman until the nail is removed