Terrains that can damage the player will do twice as much damage as normal. The game occasionally creates both invisible walls and walls which seem normal but are passable by both the player and monsters. Greater vaults are half as likely. Random vaults are more likely. Lesser vaults are unchanged.
Mutations are more likely to be nasty.
You will be subjected to an invocation of the Ancient and Foul Curse each midnight and randomly throughout the day. Temporary and permanent resistances are not cumulative. Word of Recall will occasionally reset your recall depth to random dungeon level.