There are plenty of synonyms for the phrase "on fire" that can make your writing more exciting and engaging. Some options include "blazing," "ignited," "ablaze," "alight," and "enkindled." You could also use words such as "burning, smoking," or "flaming" to convey similar meaning. For a more metaphorical approach, consider using terms like "bursting," "exploding," or "boiling over" to describe a person or situation that is creating a lot of excitement or energy. Whether you're writing about a competitive sports game or trying to spice up a description of a new product, using interesting and varied synonyms can help keep your readers engaged and entertained.