Done by (someone).

Belonging to oneself and to nobody else.

to the rescue

crucial moment, especially in which one can finally show his potential or must reckon with something / moment of death

Achieved by the operation of one's personal strengths and merits.

(informal) To get what's coming to one; to receive one's comeuppance; to suffer the undesirable consequences of one's misdeeds.

(idiomatic) At one's disposition; easily controlled by someone due to their power, affluence, charm, etc.

Belonging to one.

(idiomatic) Alone; without aid or accompaniment.

Alternative form of on one's lonesome