The phrase "cast a gloom upon" is often used to describe the act of bringing a negative or depressing atmosphere into a situation. There are many synonyms that can be used to express the same sentiment, such as "darken", "shadow", "taint", "sadden", "depress", "embitter", "dampen", "stifle", "overcast", "cloud", and "lower". Each of these words can be used in different contexts, depending on the intensity of the situation and the intended effect. Using these synonyms can help to add variety and nuance to your writing, and can help you to better convey the emotions and atmosphere of a situation to your readers.