Seize the Day
Sorcery
Untap target creature. After this main phase, there is an additional combat phase followed by an additional main phase.
Flashback 
(You may cast this card from your graveyard for its flashback cost. Then exile it.)
イラスト：
Secret Lair Drop#1172レア英語適正
裁定
2018年12月7日
Seize the Day can target a creature that’s already untapped.
2018年12月7日
If the target creature becomes an illegal target for Seize the Day, the spell doesn’t resolve. There isn’t an additional combat phase or main phase.
2018年12月7日
If you somehow cast Seize the Day during an opponent’s main phase, that opponent attacks during the resulting combat phase, since it’s still that player’s turn. If you somehow cast it not during a main phase at all, all that happens is you untap the target creature.