House Baratheon. Loyal.
Location. Cost: 3.

Dragonstone. Stronghold.

Reaction: After a phase begins, kneel Dragonstone Castle to choose a character. Until the end of the phase, that character cannot stand.

The Valyrians had raised it, after all, and all their work stank of sorcery
Ted Nasmith
Favor of the Old Gods #68.

Link: Decklists

Dragonstone Castle

Rules FAQ

The Castle reacts to a phase beginning, and thus occurs during step X.1 of the phase. This means that, for example, if the Castle is used during the Standing phase, it will trigger before any card stands, and therefore the target will remain knelt while the Castle will stand.