Each opponent in turn order chooses a card to discard without revealing it, then all the chosen cards are discarded simultaneously. No one sees what the other players are discarding before deciding which card to discard.

If there are multiple cards tied for the highest mana value, each player who discarded one of those cards will lose life equal to that mana value.

If Scythe Specter deals combat damage to multiple players simultaneously (perhaps because some of the combat damage was redirected to another player), its ability will trigger for each of those players.

In a Two-Headed Giant game, each member of the opposing team will be able to see the other's hand before deciding what to discard. If each member discards a card with the same mana value, each player will lose that much life, resulting in the team losing life equal to twice that mana value.