Sonic 3 & Knuckles Part 2: Hydrocity Zone (Knuckles)
606I did a bit of backtracking to get to other areas in to make sure that every Special Stage ring could be found by Knuckles in Hydrocity. I was a bit lazy in some of them, but I was still able to get 4 more Chaos Emeralds throughout the whole zone. I just need one more.
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Act 2 has a change in routes when Knuckles reaches the place where he drops Sonic & Tails into a pit. He can break through the wall he was behind before and can continue on from there.
His Egg Robo version of Act 2's boss is able to swirl up water to his machine without having to first descend towards the surface. Since Knuckles has a lower jump, he has to rely even more on the boost he gets from the water bombs Egg Robo drops. Either way, his exit to Marble Garden is the same as Sonic's & Tails'.
The physics of the bombs' boost can make it so that Knuckles will leap skyward, even when he got hit by one. Since he was underwater at that point, this made him fly high, all while the game still treated him as being underwater.
Really. If you do this just before your character drowns, he'll drown in midair, most likely starting from outside the top of the screen.
Here's the glitch in action:
http://www.youtube.com/watch?v=uGMnzftrODI