Helios Passwords:

At Helios, enter "GIFT" or "OGRE" to get some items. The password to open the door is "FATE".

The Secret Lens Shop:

The Lens Shop is located on a small white island just south from Hermez Village. Just walk to the forest and you will find it.

Multi-player mode:

Collect a Channel Ring and equip it on the character below Stahn. Press Select on controller two to use that port to control that character. Repeat this code on other characters to use more controllers via a multi-tap.