"对方开挂了"在英文中表达为"The other person is using cheats/hacks."
来源是网络游戏中，开挂就是使用一些不正当手段，如外挂软件来获徖游戏中的优势。
例句：
"I can't bepeve he's using cheats in this game, he's such a hacker." (我不敢相信他在这个游戏中使用了作弊工具，他真是个黑客)
"I'm pretty sure the other team is using some kind of hack, they're winning too easily." (我很确定对方队伍在使用某种外挂，他们赢得太容易了)
"I got kicked from the game for using cheats, but I swear I didn't do anything wrong." (我因为使用作弊工具被踢出了游戏，但我发誓我没做错任何事)