You never know if theyre going to have some weird instant speed lifegain spell or something to prevent damage
But for other Rooms where both abilities are one-use, or more context-dependent effects, there will likely be a dynamic choice about which order to unlock the doors every time theyre played
Reducing a creatures toughness to 0 means its put into the graveyard the next time state-based actions are checked, usually before a player gains priority
The Unfathomable Crushing Brutality of Basic Lands - Black and white, metal (the style, not the material) versions of the five Basic Land cards
If you are using it defensively to protect your own spells on your turn, I would cast it in your second main phase, especially if you do not care about attacking
Consequently, the fact that Death's Majesty makes all Zombie creatures is very good since her ultimate becomes a one-sided board wipe that will likely win you the game on the spot