As the third mode is performed, first the player whose turn it is chooses two creatures they control, then each other player in turn order does the same, knowing the choices made before them. Then all the chosen creatures are sacrificed at the same time.

As the first mode is performed, first the player whose turn it is chooses two cards in hand without revealing them, then each other player in turn order does the same. Then the chosen cards are discarded at the same time.

You can choose a mode even if some or all players will be entirely or partially unaffected.