A Taming Gem is one of the first items you'll become familiar with in Mighty Monsters.
Taming Gems, currently, can only be acquired from Treasure Chests or purchased with 
Diamonds.
You can also get Taming Gems as a Quest reward.
Taming Gems are used to capture other monsters in Battle, however they have a few limitations.
Taming Gems can ONLY capture Stage 1 Monsters, and as such, function only in the Normal mode of any of the Islands.
Taming Gems can only have a certain percentage chance of successfully capturing an enemy monster.
- Common Monsters can have up to a 75% capture rate
- Rare Monsters can have up to a 40% capture rate
- Epic Monsters can have up to a 15% capture rate
If you should run out of Taming Gems during battle, or you simply would like to avoid failed capture, you can purchase one of the Master Gems with Diamonds.