This is Relm's sketch bug. It can also be accomplished by sketching Gau when he returns from leaping on an enemy in the Veldt. Nine out of the tens times you do it your game will lock up and you'll have to reset, so be sure you've saved first. You also have to be very careful because it can do anything from botch up your inventory to delete the save file.
That's the Intangir and it's located on Triangle Island at the upper-right corner of the world map.