The Gem of Ermac is a magical emerald gem in a small part gold, part silver medal belonging to the ninja warrior Ermac, and it first appeared on his forehead in Mortal Kombat: Deception and reappeared as the 21st Relic under the name "Ermac's Gem" within the Konquest mode of Mortal Kombat: Armageddon. It can be found in Arctika.
Legend says that this mystical emerald gem increases Ermac's telekinetic power ten-fold. This gem is also said to harness great telekinetic energy within its shell.
Ermac's Gem returns still on Ermac's forehead within his updated costume in Mortal Kombat (2011). It is a little smaller this time.