The Magic Amulet is No Heart's primary source of magic and power. Not much is known about it.
It is very simple in design, being a round red stone (referred to as a "lightning crystal") on a metal (possibly silver) triangle. The gem sometimes glows red when No Heart's eyes glow.
In the comics, the gem sometimes is green and the metal is red.
CreationNot much is known about how No Heart created it, but it came out of his cauldron once it was finished.
Later, when he must get a replacement for it after Beastly accidentally broke it, he simply enters the room with the new amulet, and states that he found the crystal, suggesting the the crystal itself had to be located somewhere. It is possible, he dug it out of the ground somewhere.
In it's first appearance, this device deflects the power of the Care Bear Stare, making No Heart immune to it. However, this only worked once, and never served this purpose since.
Although it is used by No Heart, Beastly uses it at one point after it breaks. What was possible, because No Heart left the castle and didn't see Beastly fooling around with it. During the same episode, No Heart finds a pendant identical to it in appearance, but ten times more powerful. This extra power is not demonstrated in future episodes at any times.