An adverb meaning 'perhaps' or 'possibly'; used when the speaker is making a guess or suggestion (similar to 'by any chance').
もしかして、今日はテストだったのを忘れた？
Could it be that you forgot there was a test today?
もしかして彼女、もう帰ったのかな。
Maybe she has already gone home.
もしかして、それは昔の友達の話ですか？
By any chance, is that a story about an old friend?
Used to indicate a condition ('if' or 'in case'). In practice the speculative sense is more common, but context can render it conditional.
もしかして雨が降るなら、ピクニックは中止になります。
If it rains, the picnic will be canceled.
もしかして都合が悪ければ、別の日に変えましょう。
If it's inconvenient for you, let's change it to another day.