Antares Snipe

Heavenly Scorpion Shot. Archer of “Black”'s trump card, a sniping Noble Phantasm that shoots a shining star. It is a conceptual materialization of the Sagittarius constellation, but it is not as if it cannot activate without the constellation present. It has a tracking ability, naturally, and it doesn't even need for its true name to be released or for it to be filled with mana in order to activate. After all, as long as there is a night sky, “the star of the archer always aims at the scorpion,” and so it only requires for him to move his fingers away from the already drawn bow. It has a secondary effect, but, like in the novels, there is extremely little chance of it being spoken of even if the Noble Phantasm is used. However, it can only shoot once every night. Considering the average length of a normal Holy Grail War, he would be limited to using it about fourteen times.
Though its rank is high, it has the weakness of not having attack power worthy of special mention, so he has to try to achieve a one-shot kill as much as possible each time he uses it.
In his battle against Mordred, Archer could not see any weak points in her armor and feared that she might escape after he used it, so he withheld using the Noble Phantasm.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia