I have never heard of the Emergency 921 Chaplet novena to the Mother of Mercy. The closest thing I found was the Mother of Mercy Novena from this website:
It should be noted that on the home page it states:
Urgent Messages From God The Father, Jesus, Mary, St. Joseph And St. Gabriel through Chris Courtis, a visionary in Maryland, U.S.A. Distributed by The Moving Heart Foundation.
You should only say novenas and Chaplets (especially from so-called visionaries) that have been approved by a bishop. They would usually have some mark of approval from the bishop. This mark of approval only means they are theologically sound and not necessarily that the claimed efficacy of the prayer is true.
The Church would only approve private revelations as being not harmful to the faithful and, even then, they are optional for one to believe. For example, though I highly encourage visitors to our site to pray the Rosary, there is no requirement that any Catholic has to pray the Rosary.
Instead of choosing a novena that, to my knowledge, has not been approved by a bishop, choose one that has been, like the Chaplet of Divine Mercy:
I hope this helps,