Test Menu

During any time during the game, simultaneously press and hold the A, B and C buttons and press Start on controller 2.

A test menu should appear with Input, Sound and C.R.T tests. And when you exit, it will send you back to the Sega logo screen.

Super Strength/ Virtual Invincibility

For this cheat, you need a cursed weapon/suit of armor. Also, having Rafael's Stick helps save some cash, but you don't absolutely need it. Also, if you want the effects to be permanent, your level has to be maxed at 31.

Equip the cursed weapon/armor. Now, either use Rafael's Stick or talk to a priest to remove the curse. Your strength or armor class (depending on what you equipped that was cursed) will go down. Keep re-equipping and removing the cursed item until your Strength/Armor Class goes to a ridiculous #, like 9999 or something like that. Now, re-equip your most powerful weapon/armor, and you'll either kill enemies in one hit guaranteed (Super Strength), or take only 1 damage from any attack from any enemy, including bosses (Invincibility)