Access New Game+ without playing twice 
     To  be  able  to access New Game+ without having to play the game
twice, complete the game all the way past the six elementer pillars in
Shisel's Castle. Then activate the lift. Enter the dungeon, but DO NOT
go  any  furthur  than  the first screen. It should look like a purple
stairway.  Then,  simply exit the dungeon the same way you came in and
your file should be in New Game+ mode.

New Game+ 
     To access the New Game+ mode, successfully complete the game once
and  save.  When  you  restart  the  game, you will have the option to
choose New Game+. New Game+ allows access to a bonus dungeon and a new
difficulty level.