A conjunction used to add information or emphasize an additional fact (equivalent to "moreover" or "furthermore").
彼は仕事が早い。しかも正確性も高い。
He works quickly. Moreover, his accuracy is high.
この店は安い。しかも品ぞろえがいいから人気だ。
This shop is cheap. Furthermore, it has a good selection, so it's popular.
彼女は英語が話せる。しかも中国語も流暢だ。
She can speak English. Furthermore, she is fluent in Chinese as well.
A conjunction used to add a fact that contrasts with or is surprising given the previous statement (similar to "nevertheless" or "and yet").
試験勉強はした。しかもよく準備したのに、結果は振るわなかった。
I studied for the exam. And yet, despite preparing well, the results were disappointing.
彼は約束を忘れた。しかも謝りもしなかった。
He forgot the appointment. What's more, he didn't even apologize.