Purim Riddle

See if your child can guess the riddle:

I whispered words that sealed his doom,
A man of power, now met his tomb.
Though high he soared, I saw his fall,
And urged him to his final call.

A plot was hatched to see a throne,
Yet, in the end, his pride was shown.
I spoke of gallows tall and high,
Where fate would hang, and dreams would die.

Not of the crown, nor of the feast,
Yet in my counsel, death increased.
Who am I, whose name is rarely known,
But in the shadows, power was sown?

Who am I?

• זרש (Zeresh)