The phrase "wast mercy of" implies a lack of compassion or pity towards someone or something. There are several synonyms that can be used to replace this phrase, such as "indifferent to," "unsympathetic towards," or "hard-hearted." Other synonyms include "callous," "cold," and "unfeeling," all of which convey a sense of emotional detachment or a lack of empathy. Similarly, one could also use the phrase "devoid of mercy" to indicate a complete absence of compassion or kindness. No matter which synonym is used, the message remains clear: the individual in question lacks the ability to empathize or show mercy towards others.