I had this idea for a unique gem that could be won in a special challenge. I call it the Shield Gem.
The challenge it can be won from is called Impenetrable Defense. The goal is to get as many 0 stars on your base as you can.
The gem won has the properties that when it is placed in a ritual with 2 other gems, at the end of the ritual the 2 gems will remain in the totem and the shield gem will gain no value.
You also get a new potion called the shield potion. This potion can be triggered once you start a ritual, and lasts for however long the ritual lasts for (usually 12 hours). During this time, everyone who reaches your totem will find that the probability for stealing your gem at all stars is halved (50% to 25%, 5% to 2.5%). Of course, it cannot be retrieved if stolen.
If your ritual is interrupted, the potion's effects will also stop and must be continued if you resume the ritual. The time remaining on the potion's effect will exactly match the time left on the ritual. Note that this will also take into account the Ritual Berserker.
This special defense potion can be found in fake keyholes at a third of the probability of finding other potions, and can also be bought for 21 orbs if you have none.