You know, while I was attempting to design a level, I realized just how weird the Turret enemy is. No matter how far you think you're away from its trigger radius, no matter how high you get above it, and no matter how hard you try to block it off by using the "Impassible" or "Block Enemies" effects on linedefs, these things are ruthless. You can't even kill them unless you crush them. If Robotnik had only used the Turret enemies, he could've possibly won.