Sonic Blast: Part 3: Red Volcano Zone (Sonic)
21Red Volcano looks more like Purple Volcano with main color of its graphics being such. Regardless, its Act 2 Special Stage contains the Red Chaos Emerald.
This level feels like a soft mix between Lava Reef and Volcano Valley. There are machines you can operate to do things like sail you across the lava, or scale a wall.
It's kinda slimy that this Zone's Act 1 Special Stage Ring is practically right above the goal post. If you miss the jump to it, you likely won't get another shot. Either way, that Special Stage doesn't have the Chaos Emerald, anyway.
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For Act 3, you have to make your way up to the very top. You eventually reach a platform that flies you up to pitch black darkness, and then you have to fight Eggman this way.
He uses a giant pogo stick contraption that can also sling a boulder at you. You need to hit the glass of his machine while trying as much as you can not to get hit by that boulder.
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Knuckles Playthrough:
https://youtu.be/Vp_VLRFn4sk