Guilty gear X - Advance Edition.
Don't get me wrong, console Guilty gear games are awesome, and damn hard too. GGX Advance, on the other hand, Is shit simply because:
a) The enemy AI on one-player is a joke. The whole game can be beat without using any continues on hard - In fact, the whole game can probably be beat without losing any life. At first I was all like ''Yeah! Guilty Gear! On my Gameboy!'' but theres no challenge.
Theres no point playing multiplayer if you have a console version of Guilty gear. In fact, theres almost no point playing this if you've got a console version.
However, Its guilty gear, and its pretty useful for practicing. Its also a slight challenge if you go someone your crap with, In my case, Potemkin or Milla Rage. And its also really good for Guilty Gear noobs, as they can learn the basic techniques without getting their ass kicked on the 3rd round of Arcade mode.