Near the end of the game, equip an Elemental Spirit then speak to it in the Mana Village. Successfully complete its quest to meet the Benevodon of the same element in another dungeon. Do the same thing for the other seven Elemental Spirits to get a total of eight Lex items. Successfully complete the game after you have done this. When the game resumes at the Mana Village, the Mana Tree mural will glow. Enter it to teleport to a bonus section of the last dungeon.
Key to Haunted House
When you are in the room with moti, go over near the fireplace. There should be a coatrack by it. If it is sparkling, press a and it should say something like "You obatin the Hidden Key". Go out to the Haunted House (which should be right under Moti's house) and open the door.
Legend Of Mana reference
At the beginning of the game, when you deliver the letter to Motti a miner named Watts will enter the house. He will start saying something about the gems. Watts is the miner that you helped find his happer in Legend Of Mana.