During the gameplay press 't' to bring up the chat line. Then enter:
Code                Result 
/godmode        God Mode 
/nextlevel        Skip to Next Level 
/room #            Teleport to Room # 
/spawn #         Spawn Object # 
/moregold        Add 100 Gold 
/tinymonsters   Tiny Monsters 
/tinyplayers      Tiny Players 
/insanity           Monsters Attack Each Other 
/repeat             Repeat Last Cheat Entered