Got Maid Costume into the Currently Final Dungeon by going through the castle town and taking the Ninja way back into the Ring room then going into the dungeon from there? I forget if the costume reset after I lost the battle.
NoteToSelf: Remember to maybe buy a Castle Town meal to maybe help win against the mid boss, since those sit-down meals have unique effects? Maybe the Lucky Tea... Dunno what being Lucky does in combat.
Note that the Regalle Woods Ring would be the only Ring that'd probably send Brill into combat immediately on exiting?