If cheat codes existed, and you HAD to use them...
The Real Unstoppable:
When applied, your defense and attacks are increased so that everything can be killed in one hit. Also, powerful attacks against you actually heal you instead of damage you.
(Imagines using this in The Hive) *grin*

Lady-Dee: Hey my fat keeps me warm in the winter and shady in the summer.
If anyone played Turok 64 they'd probably remember disco mode, so disco mode.
edit: SONIC VIBRATIONS: CREATE DESIRE: TO PARTY
If I had to use cheat codes?
All Temp Powers, No Aggro Cap, Immediate Recharge
Just go around and kill everything... Including GMs with infinite nukes.

/Idonthavetimeforthis
Causes all missions to be 30 feet from you.
/pinatapunch
Every time you defeat an enemy, they explode into candy.
/alternate form (Kronos)
The code where you get to dress up like a chef:
Changes the animations of Sonic Blast to the character air-guitaring.
/leadvocals which would give a Sonic users a microphone.
@craggy see me on Union for TFs, SFs (please!) or just some good ol fashioned teaming.