Status: Black is dead as it stands. Both sides should play elsewhere. (Black has two ko threats inside here.)
Black playing first can't change the dead status.
does not work, since
almost fills with a bulky five and Black is dead.
at a does not work for the same reason.
throw-in fails too. Black can't play at a for shortage of liberties. He could make life in this way if he had one or more outside liberty.
Of course, White should play elsewhere (tenuki). We can observe three classes of possible blunders here: