Urabrask the Hidden {3RR} |Legendary Creature -- Praetor| 4/4 Creatures you control have haste. / Creatures your opponents control enter the battlefield tapped.
Twilight's Call {4BB} |Sorcery| You may cast Twilight's Call any time you could cast an instant if you pay 2 more to cast it. / Each player returns all creature cards from his or her graveyard to the battlefield.
Eureka {2GG} |Sorcery| Starting with you, each player may put a permanent card from his or her hand onto the battlefield. Repeat this process until no one puts a card onto the battlefield.
Urabrask's ability creates a replacement effect. It replaces your opponents' creatures entering the battlefield with those creatures entering the battlefield tapped. As such, it applies to those creatures before they're on the battlefield. For this to be possible, the ability has to be around before those creatures are on the battlefield. So if Urabrask is entering the battlefield at the same time, there's no ability to cause the other creatures to enter tapped. A card like Twilight's Call or Show and Tell causes multiple permanents to enter simultaneously.
In the case of a Eureka or Thieves' Auction, the permanents do not enter the battlefield simultaneously. They enter sequentially. So if Urabrask is already on the battlefield when the opponents' creatures enter, they'll enter tapped. If Urabrask doesn't enter until later, then the opponents' creatures are already on the battlefield and won't be affected by his ability.
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