Great, and here's a walkthrough
Mecha shouldn't be a problem. With Eggman your first must be PROTECT, then when MEC(Master Emerald Cannon) isn't open use ATTACK and wehen it opens (sorry for my english) First use your SP ONLY when it is open (when closed after the beam go back to ATTACK)when you don't have any SP anymore and it opens up use PURPLE VORTEX and when your health is under 2000 use HEALER, that's how I have beaten Eggie and retrieved the Master Emerald. By the way, the password actually is Nightmare, but i don't know how it could be that in isn't working(once again sorry for my English but i'm from The Netherlands(or Holland however you guys call it)) so when want to skip the battle go to the scene select and the password for the last scene is "Reala"