bad = 不好,糟糕
worse = 更不好,更糟糕
worst = 最不好,最糟糕
bad 独立形容词Absolute Adjective.
It's performance is bad.
它的表现不好
badly 附加副词Additive Adverb
It performed badly.
它表现得不好
以中文很难解释,bad 和 badly意思一样,但这是语法上的不同.