First select Super T mode. Next have your cursor on Ryu for 1-5 seconds, then do the same for T. Hawk, Guile, and Cammy in that order, the last person to highlight will be Ryu again. Once you've highlighted Ryu for the duration of time, press Back Button, then you will have less then a second to press LP, MP, HP all at the same time. If the character you have choosen has a black shadow portrait and no name you now have enabled Akuma for the battle. If you wish to use Akuma again, just repeat the process.