"Is mercy of" is a phrase that denotes a state of being under the control or influence of someone or something, often in a way that entails being granted mercy or leniency. There are several synonyms that can be used in place of this phrase, depending on the context of the sentence. Some examples include: subject to, at the behest of, in the hands of, under the sway of, and at the mercy of. Each of these phrases conveys a similar meaning to "is mercy of," but may emphasize different aspects of the situation, such as vulnerability, control, or power dynamics.