Coal Mine is the third challenge in Challenge mode. It becomes available by completing the first puzzle of Spectrum. The puzzles of Coal Mine involve clearing specific numbers of Coals in one move each. Certain puzzles also prohibit the use of Lightning Gems; clearing them negates any progress made toward the puzzle status. However, no penalties occur for creating Lightning Gems in those puzzles. Completing the first puzzle of Coal Mine unlocks Chain Reaction, the next challenge in Challenge mode.