1) Find a bonus round in each world (Cemetary, New Toonland, etc.)
2) Achieve a perfect score in each round (you don't have to get a perfect score in each round; 27 out of 30 barrels will do.
3) When you've beaten all 5 bonus rounds with perfect scores, you get all five pieces to the Planet X remote.
4) If you get a Planet X remote piece and then you die before you finish the level, you still keep the remote piece.
5) You have to collect all 5 pieces in one play session