How do you get supershadow in sonic robo blast 2

First of all, Shadow is not a character initially in SRB2. You must download a .wad file of Shadow and add it by pressing the ~ key on the title screen and typing "addfile wadfiel.wad." If you have the right variation of the wad, then Shadow will transform when 50 rings are obtained and you jump twice after getting the 7 emeralds, just like Sonic does.