Yes, 3D Blast introduced the homing attack (albeit in a very different implementation than what was used going forward), but I don’t think anyone considers Rush mainline, and that introduced the boost. I don’t think 3D Blast is mainline, but to be honest, I can’t think of any legitimate set of rules that would exclude it without also excluding Sonic 4 or Mania. It’s just a feeling I’ve got. The best I can give is that, if it is mainline, it’s the only mainline Genesis game Sega hasn’t done any work on to improve. 1, 2, 3&K, and CD have all gotten post-mortem remakes, 3D Blast only has contemporary ports and emulation. Yes, this does also exclude Chaotix. If that game was important, Sega would have rereleased it once (I don’t think GameTap counts). Jury's still out on where I think Shadow falls.