The phrase "most mingling" can be replaced with a variety of synonyms depending on the intended context. Some potential alternatives include "highly socializing," "most gregarious," "extremely sociable," "very outgoing," "incredibly friendly," and "exceptionally convivial." These phrases all suggest that someone is comfortable among others and enjoys socializing, which can be useful for describing a person or a particular type of event. Other potential synonyms could include "most social," "most interactive," or "most engaged," depending on the specific emphasis that the phrase is meant to convey. Whatever synonym is chosen, it should reflect the social nature of the person or activity in question.