Crush3D - gamefront.com

Set within a 3D world, players use the game‘s unique crush mechanic to “crush” the environment and transform it into a more simplified 2D platformer. Once flattened, players utilize the 2D space to move to new areas to solve otherwise impossible challenges, and unlock secret items that were previously unobtainable in the 3D environment. Players then “uncrush” the 2D environment and return to the 3D world.