to get akuma get 5000 vs points (alot of his moves are like ryu's)
If you get to 9999 vs. points you unlock a stronger form of Akuma. He is stronger and faster. He shoots two fireballs when he jumps into the air instead of one. Other than that he is an exact replica of the other Akuma you obtain at 5000 vs. points.
To get a character's alternate costume, highlight them when you are selecting a fighter in any mode, and press A+B. You must hit them at the exactly same time for this to work. It may be kind of tough, but it'll work if you do it right.
For Easy moves, during a fight press Select. A sound will confirm it. Then you can do all the moves easily.
Fireball: Towards Opponent + Punch
Super Fireball: Away from Opponent + Punch
Dragon punch: Down + Punch
Hurricane Kick: Away from opponent + Kick
Easy Special Moves
If you are having trouble pulling off your favorite character's special moves on the small GBA controls, this code can help you out a bit.
During a 1p game, tap Up Up Down Down Left Right Left Right B then A without pausing the game. You need to do it very quickly.
Once the code has been entered you will be able to pull off special moves by simply tapping a direction on the D-pad and the correct button.