Defeat Cubia:
Bring Mistral and Piros and make sure you are at least at level 36. Don't attack Cubia head-on, you have to destroy the core. The core sends out miniature cores which need to be dealt with first. Destroy all the 'Repth' cubias first and then all of the attacking ones, leaving only 1 left. Now you can attack the core.
Defeating Martina R:
First use the Moon scrool on Martina R to put her to sleep. Next use the Beast Bane item on her (trade for it with NPC Koji) to take down here magical defenses. Now you can inflict magical damage to her. Use summoning scrools and she should go down quickly.
Baby Gruntys:
In most root towns you will find a baby grunty. If you feed one of these babies a lot of the food you can get in the field it will eventually become an adult and give you the grunty flute. Use the flute on the field and the grunty will come to help as long as you are both in the same server.
Extra health and key items:
After beating the game, go back to the first root town and visit Haunted "Forbidden Holy Ground" four times. Each time you see a special cut scene from the show .Hack//Sign. You also get a special key item and a golden or silver grunty that will increase your health and magic strength.
