Unused graphics: ice rock and ice block

Two more unused sprites, this time in Icecap Zone. One of the PLCs from act 1 contains what appears to be a large ice boulder. No object in the final game uses the sprite, but the mappings are still in the ROM and... this thing is huge.

The mappings cleverly reuse the same pieces in the top and bottom halves of the sprite, as to maximize its size without using up too many tiles. It fits snugly in act 1's narrow corridors, so maybe that's where it was meant to be used.

The second sprite is present in both acts, and has a fully-functional object associated with it, which can be placed using debug mode. It's a square block that breaks when you jump on it, similar to an obstacle used in Sonic 1's Marble Zone.

Its size and appearance suggest it was meant to be placed in the chutes which lead into act 2's underground area. The final game plugs up the top of these chutes using a different object, which is in turn lifted from Sonic 2's Hill Top Zone.