Looking on the internet deeply has found these results:

at the ??????? of is the most popular phrase on the web.

at the mercy of 114,200,000 results on the web	at the ??????? of 12,970,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
These days, workers are at the mercy of frequent and risky employment transitions. European gas consumers cannot be left at the mercy of monopolies. You live at the mercy of forces outside your control... Killing you at the mercy of a noble fish. We know that thousands of women are literally at the mercy of slave traders. You left me at the mercy of those Kandorians. In fact, I ran away, leaving Francesca at the mercy of the hyena. I'm at the mercy of this madman.	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

at the mercy of

114,200,000 results on the web

at the ??????? of

12,970,000,000 results on the web

More popular!

These days, workers are at the mercy of frequent and risky employment transitions.
European gas consumers cannot be left at the mercy of monopolies.
You live at the mercy of forces outside your control...
Killing you at the mercy of a noble fish.
We know that thousands of women are literally at the mercy of slave traders.
You left me at the mercy of those Kandorians.
In fact, I ran away, leaving Francesca at the mercy of the hyena.
I'm at the mercy of this madman.

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.