Not many people saw this one coming. Nintendo announced that a new Mario RPG is in development for the Game Boy Advance, and a short, playable demo was at E3 today.

The game, entitled Mario and Luigi, kicks off when an evil witch steals Princess Peach's voice, replacing it with explosives. Being the most vengeful plumbers ever, Mario and Luigi take off after the witch. In an unusual twist, our heroes team up with their old foe, Bowser, who had just arrived for his regularly scheduled kidnapping of the princess. Shortly after the journy's beginning, Mario, Luigi, and Bowser's ship is ambushed from above and Bowser becomes separated from the others. Now the brothers must traverse strange lands and fend off enemies in search of the evil one--familiar territory for these two.

Mario & Luigi gives players the ability to control the characters separately, or use Mario and Luigi simultaneously to perform powerful "super moves." Much like the original Super Mario RPG, both platform and RPG elements will make up the gameplay formula.

RPGamer's Doug Hill discusses his first impression of the game here.