(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)
When you unlock this door, manifest dread.

(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)
Whenever you attack, target attacking creature gains double strike until end of turn.