"Reigns supreme" is a phrase often used to describe something that is in complete control or has complete dominance. However, there are many other ways to express this sentiment. "Dominates," "rules," "completely owns," "holds sway," "triumphs," and "prevails" are all excellent synonyms that can be used in place of "reigns supreme" for added variety and impact in communication. Each of these words carries a slightly different connotation and tone, so choose the one that best suits the situation and message you are trying to convey. Regardless of the word chosen, these synonyms convey a sense of total control and authority.