Why is there a carnival zone on Angel Island of all places?? Did Robotnik have time to just build one? That always bugged me, the rest of the zones made relative sense in one way or another (despite, you know, radically different climates being right next to each other on a floating island).
I'd guess it was one of the most recent things that the Echidna civilization built before they disappeared. Knuckles maintained it because he was all alone on the island; the carnival and its maintenance were his only sources of amusement.
It's the surrealism of the Mega Drive trilogy (+ Sonic the Hedgehog CD). Spring Yard didn't follow a level theme (It wasn't really a city level, it wasn't a casino level, and it wasn't a mountain level...), Collision Chaos is a pinball table... "On drugs", and Carnival Night looks out of place in Angel Island. Actually, Sonic 3 has the most "normal" levels in the trilogy, so Carnival Night looks even more out of place.
Alternatively, Carnival Night is Eggman's primary base on the island, while Launch Base is just the subset dedicated to getting the Death Egg airborne again. The Flying Battery's gotta refuel somewhere, and the level order was originally going to have Flying Battery immediately after Carnival Night, anyway...
Why do the spitting statues in marble garden appear human?
Without knowing who built them, it's impossible to say. Humans could have built them. Or, just as humans make animal statues, anthropomorphic animals could build human statues. They might be religious.
It was built by Echidnas who have probably never heard of humans.
How did Knuckles knock Sonic out of Super Sonic mode? He even did so hard enough to knock the Chaos Emeralds out of Sonic. Isn't Super Sonic supposed to be invincible, at least for the early games?
Better question. Why does he hide the stolen emeralds in poorly hidden giant floating minigame rings?
Maybe being guardian of the Master Emerald just let's him do h4x shit like that? For all we know, canceling a Chaos Emerald-induced Super Mode is part that power set, like sensing Emeralds - not like he's ever had occasion to do it again.
Actually, in one of the cut-scenes in Sonic and Knuckles, Knuckles knocks a giant boulder into Sonic, which can revert him back to normal from HYPER. Since he's an NPC in Sonic's story, he's invincible in cut-scenes, but a joke in actual battle.
It's never stated how long Knuckles' story takes place after Sonic's plus in the story for the Japanese version of the game they never do say anything concerning Knuckles' adventure or the whole Eggrobo throwing a bomb at him, in the Japanese manual for both Sonic 3 and Sonic & Knuckles only the events of Sonic's story of him coming to Angel Island and the Death Egg crash landing after it's take off at Launch Base are ever told in the Japanese manual while like I said Knuckles' story with him fighting Eggrobo is never even mentioned. Also like I said they never stated how long after Sonic's story it takes place after, it could be months or even a year or more, I mean games don't have to follow the timeline of how many years between their releases it's been, I mean apparently Sonic CD takes place before Sonic 2 despite the fact the former was out first. I mean it could have been long enough for the forest to grow back and be burned again, I mean not all video games don't necessarily always have to go by reality's clock.
Why did Angel Island fall from the sky in Sonic 3 anyway? The Master Emerald was still in Hidden Palace at that time.
Eggman's ship crashed into it, and the sudden force propelled it down.