Liminality DVD Easter Egg - Timeline 
In the Title Menu, select Data. Then highlight Main. Press Right, then Left. You then receive instructions on how to operate the Gallery. These controls work for the timeline. (The timeline goes from Late 20th Century to approx. 2009. Obviously, this is the storyline's timeline.) 

DVD special keywords:
The OVA that comes with the game has hidden keywords to help you. The only one that has relevance is "Chosen Hopeless Nothingness", which is where you fight the final Boss. If you turn on subtitles, you will find keywords throughout the DVD. Some include "Luscious Her Remnant", "Hideous Organ market Scaffold, and "Dog Dancing Passionate Tri Pansy". None of them are that special, but in "Dog dancing Tri Pansy", if you reach the statue of Gott at the end of the dungeon you will get an Ice Block that is used for trading. 


Parody Mode, Mummy Ship, Goblin Summon 
To access Parody Mode, .hack with funny dialoug, the Mummy Ship with extra boss, and the Goblin Summon, simply beat the game. (JP Version Only)

After beating the game, you will get a mail from Bandai telling you the location of the Mummy ship. Inside the Mummy ship is an extra boss. 

Also after beating the game, on the BBS is the final goblin location. Beat the goblin, and equip all the other Goblin equipment. You can now summon a yellow goblin to attack. 

Difficult levels:
Go to the Chaos Gate then enter one of the following new keywords. "[ all data]" for Closed Oblivios Twin Hills, level 22, "Collapsed pagan march" for level 26, "Caressed silent melody" for level 26, "Quite gluttonous fiery sands" for level 24, "Lonely hot-blooded sunny demon" for level 27, and "Lonely hot-blooded melody" for level 30.

Defeating the Goblin Kings:
Going through a set number of events, a message will appear on the board called "Let's Play Tag". In this message, there will be a Golden Goblin challenging you to play tag. Go to the area instructed and try to defeat him. When you win, he will tell you how he is just an apprentice of the four Goblin Kings. Later, you will get extensions of the challenge note from one of the four Goblin Kings. To defeat them, get close enough to use a multi-hit attack, such as Tiger Claw or Staccato, after using an item or technique to raise your accuracy. Otherwise, most of the hits will miss. Repeat this a few times and you should defeat them easily.