Go to the mat with is a phrase used to describe a willingness to fight or contend with someone or something. If you're looking for synonyms for this phrase, you might consider using words like confront, challenge, or compete. Other related words could include battle, clash, or struggle. Depending on the context in which you're using the phrase, you could also try adapting it slightly to better suit your needs. For example, if you're talking about standing up for your beliefs, you might say that you're willing to stand your ground or hold firm. Ultimately, the key is to find a phrase that accurately captures the spirit of fighting or contending, while also sounding natural and appropriate for your specific needs.