Ermac's gem aka the Gem of Ermac
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 and still on Ermac's forehead within his updated costume in Mortal Kombat (2011). It is a little smaller this time.
Gallery
Ermac with his magical gem (Gem of Ermac)
Ermac's Gem as it appears in Mortal Kombat: Armageddon
Ermac's Gem in Konquest
Ermac with his mystic gem in Mortal Kombat (2011)
The Gem of Ermac on the forehead of hooded Ermac in Mortal Kombat (2011)
In Mortal Kombat (2011) Story Mode, Ermac can be seen wearing his Gem.