Complex sentence: Yet only his machine was actually shown in-game, where it was portrayed by a two-dimensional sprite--not until "F-Zero X" has he made an appearance that has been conveyed by a computer-generated image.
Split into simpler sentences: Yet only his machine was actually shown in-game, where it was portrayed by a two-dimensional sprite. Not until "F-Zero X" has he made an appearance that has been conveyed by a computer-generated image.