質問: what does 退始の相手がそんなんじゃねえといいな mean? what does 退始の相手がそんなんじゃねえといいな mean?
回答: "退始" is probably a typo. it maybe "退治" 退治の相手がそんなんじゃねえといいな(rude, casual) 退治する相手がそんなものでなければ良いのですが。(formal) "退治する相手" is a target person or prey whom we want to destroy. i wish that our enemy isn't such a (strong) one.