在口語中,gonna這個(gè)詞比be going to和will更地道.
“打敗”常用beat來表達(dá),如果你聽過Michael Jackson的那首Beat it就明白了.
另外,如果你愿意突出“sooner or later”,也可以將其前置.
答案就成了 Sooner or later,I gonna beat him.
Extention:但是,如果是老師布置的作業(yè),（以我對(duì)大多數(shù)中國英語老師的理解）,他們肯定用be going to 或者 will,然后再告訴你,gonna不是formal English.這是因?yàn)樗麄儫o知,只知道follow老舊的路子,不會(huì)叫你們一些地道的東西.
The writer is a A-Level student in England,the words above could only represent my personal view at the moment.