Magic Bullet Tathlum (魔弾タスラム) is a secret Magic skill of the Goldie Family Family that was secretly taught to Akechi Eimi. Only the members of the main family can learn this because acquiring this skill is necessary in order to have a right to be a successor of the Goldie Family, as Tathlum is what represents the Goldie Family. 
This magic is similar to the Shippou Families Million Edge magic, when comparing the delayed activation spells.
Tathlum was a type of ball used by the Celts as a projectile for slingshots, made from the brain and bones of dead enemies hardened with lime. The god Lugh used one to defeat the evil god Balor by piercing his Evil Eye with it.