No player may take actions between the time you choose a card and the time it's exiled.
24-01-2020
wotc
If there are no nonland cards in their hand and no cards in their graveyard, then you just lose 1 life.
24-01-2020
wotc
If you choose a card from their graveyard, it may be a land card.
24-01-2020
wotc
You must choose a card to exile if able. If there are no nonland cards in the opponent's hand, you must exile a card from their graveyard, and vice versa.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.