A proverb meaning you don't know whether the outcome or person will be harsh like a demon or kind like a Buddha — the result is unpredictable.
新しい部長の反応はまだ分からない。鬼が出るか仏が出るかだ。
We don't yet know how the new manager will react — he could be harsh or kind.
試験の合否発表の日は、鬼が出るか仏が出るかの気持ちだ。
On the day exam results are announced, it's the feeling of not knowing whether you'll get a good or bad outcome.
交渉相手によっては鬼が出るか仏が出るかだ。慎重に対応しよう。
Depending on the negotiation partner, they may be harsh or kind — let's proceed carefully.