Its the new normal for the game, having diverse characters as the norm, rather than isolated inclusion
The ladder format is the biggest reason why Ancient Tomb fetches a heavy price tag
Niv-Mizzet, Visionary The latest entry into the line of Niv-Mizzets might not be the most powerful of them, but it is still an incredible addition to the game
Cards you want to look out for are the slow lands, Sorin the Mirthless, Chandra, Dressed to Kill, Olivia, Crimson Bride, and control staple Hullbreaker Horror
Any cards I missed that you think are worthy of recognition
This can happen one of two ways: (1) the door becomes unlocked on the battlefield or (2) the door becomes unlocked as the Room enters the battlefield because you cast the corresponding half