Rotting Rats

When Rotting Rats enters, each player discards a card.
Unearth {1}{B} ({1}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Planechase

When Rotting Rats enters the battlefield, each player discards a card.
Unearth {1}{B} ({1}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave play. Unearth only as a sorcery.)

Conflux

When Rotting Rats comes into play, each player discards a card.
Unearth {1}{B} ({1}{B}: Return this card from your graveyard to play. It gains haste. Remove it from the game at end of turn or if it would leave play. Unearth only as a sorcery.)

When Rotting Rats's "enters" ability resolves, first the player whose turn it is chooses a card to discard, then each other player in turn order does the same, then all cards are discarded at the same time. No one sees what the other players are discarding before deciding which card to discard.