Y.A.G.A.C.

A very challenging and addictive 2.5D platformer game, with 2D sprites in a 3D playfield, but you are limited to movement in two dimensions. It's a story-less game, heavily gameplay based, where you play a ninja trapped in dungeons filled with traps and robots. As you collect colored balls hidden around the level, so the platforms of that color become solid and you can then reach new places inside the level.