Which word describes a tone that is grimly mocking?

The word "sardonic" is used to describe a tone that is grimly mocking or cynical. This term conveys a sense of bleak humor and is often associated with a scornful or disdainful attitude. A sardonic tone typically reflects an underlying bitterness, as it implies that the speaker is using irony or sarcasm to express criticism or derision.

In contrast, the other options represent tones that are more positive or straightforward. "Genuine" refers to something that is sincere and truthful, lacking any mockery or irony. "Playful" suggests a light-hearted or fun tone, not aligned with grimness or mockery. Lastly, "sincere" indicates a sense of honesty and earnestness, which again lacks the mocking quality inherent in sardonic comments. Thus, "sardonic" is the most fitting word for describing a tone that is both grim and mocking.