In Sonic Adventure (all versions I believe), if you let Chaos 0 kill you, you'll get a 'hint' from Tikal telling you to double tap the jump button to do a homing attack when the game restarts. Weirdly, this hint doesn't appear the first time you fight Chaos 0, and it won't appear again if you die any more than the one time. Even if you hit pause and restart it won't give you the hint again. You need to quit back to the menu and reload the save and get killed once to hear the hint again. I guess most of you haven't heard that hint before as you'd usually beat the first boss without dying. Another weird thing about the Chaos 0 battle is you start with 2 rings. This is because in the cutscene beforehand, when Sonic jumps off the police car to confront Chaos 0, he picks up 2 rings when he lands. If you die/have to restart the battle you spawn a little further back and you start with 0 rings. I'm not sure if that's intentional or not.