So I was casually looking through old concept sketches of sonic 2, until I came across this. Notice how Green Hill has a line, then Hill top is underneath it. They both share assets. We know Brenda Ross said that the desert level would have a pallete swapped ice level, which is also clearly show in this sketch. Death Egg, not shown, shares assets with Chemical Plant. What throws me off here is that "Secret Palace" has Oil Ocean zone under it. Was there more asset sharing planned? Seeing the odd floating triangles and what not in Oil Ocean does seem a bit odd. Was this zone actually a secondary zone pulled from Secret Palace? I'm trying to dig more into concept art to see if anything would even match. Seems very early in development, but interesting none the less.