A Doom Gem can be considered as a combination of a Coal, a Locked Gem, and a Bomb Gem. Like Coals, Doom Gems cannot be matched; like Locked Gems, Doom Gems cannot be moved; and like Bomb Gems, Doom Gems have a large number displayed on the front. However, unlike Bomb Gems that count down after every move, Doom Gems only count down when a move that results with no match of any gems is performed. As the number of a Doom Gem approaches zero, the Doom Gem begins to shake and emit purple glows. These characteristics intensify as the number approaches closer to zero. When the number reaches zero, the Doom Gem explodes violently, destroying everything and ending the game.
Similar to Locked Gems, Doom Gems first appear on the board in the form of a Locking Doom Gem, a basic type of gem surrounded by sparkly, violet and white-colored vapor with a swinging padlock hovering in front it. If the gem is not cleared after the next move, it will transform into a Doom Gem. If a Locking Doom Gem is cleared during the next move, the game simply continues as normal.
Because Doom Gems cannot be cleared by normal matching, Special Gems are required to do so. When a Doom Gem is cleared from the board, it explodes in a burst of smoke, violet sparkles, and small black fragments. In Classic mode, clearing a Doom Gem awards a base value of 1,000 points and adds ten to the Chain Meter of the Levelup Tube. There are no bonuses awarded for clearing Locking Doom Gems.
Doom Gems appear only in Classic mode and Challenge mode. In Classic mode, Doom Gems are first seen upon reaching the thirteenth level. On this level, the Doom Gem's number is set at 13. After the thirteenth level, Doom Gems appear once per level with their numbers set slightly closer to zero. The lowest number Doom Gems begin with in Classic mode is 9.
In Challenge mode, Doom Gems appear in the Eclipse puzzle of Chain Reaction and in every puzzle of Survivor. In the Eclipse puzzle of Chain Reaction, Doom Gems appear with their numbers set at 1 in attempt to make the puzzle more difficult. In Survivor, Doom Gems appears with their numbers set at 20 during the challenge's seven normal puzzles, while during the challenge's Eclipse puzzle Doom Gems appears with their numbers set at 15.