Hold Minus and press Up, Down, Right, Left, 1, 2 at the title screen. Carbuncle will say something to confirm correct code entry.
There are five gameplay modes that are hidden which includes: Non-Stop Fever, Excavation, Giant Puyo, Ice block, and spinner. To unlock these modes keep purchasing the item in the fourth tab of the shop until you unlock one of these modes. You must unlock all five individually this way.
To unlock all characters, all cutscenes in the gallery, and obtain 9999 points for the shop enter the following commands at the title screen. You will hear Carbuncle's voice if it was done correctly. This code does not unlock the items found in the shop but you can enter this code multiple times to regain all points spent at the shop.