When it comes to synonyms for the phrase "take on all comers," one can use several other expressions that convey the same meaning. For instance, the phrase "take on all challengers" can be used to refer to someone who is ready to face and compete against any person or team regardless of their skills, experience, or reputation. Another synonym can be "meet any opposition head-on," signifying that the individual is unafraid of confronting any challenge or obstacle and will do so directly. "Face any adversary" is yet another synonym that has the same connotation. Hence, these expressions can be used interchangeably to imply a willingness to contend with anyone who presents themselves.