Decreasing adverbs are provided in this article. The words listed here are commonly found along with the verb decreasing in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb DECREASING.
actually, constantly, continually, continuously
dramatically, exponentially, generally, gradually
greatly, monotonically, possibly, potentially
progressively, rapidly, regularly, significantly
simultaneously, slightly, slowly, steadily
strictly
Hope this word list had the decreasing adverb you were looking for. In addition to adverbs used with decreasing, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.