How about a Grief Seed? http://static.zerochan.net/Grief.Seed.full.1262516.jpg Or a Soul Gem? http://vignette4.wikia.nocookie.net/legolegendsofchima/images/1/1f/Soul_Gem.jpg/revision/latest?cb=20131125020755 ^.^ (Design them however you like, no two of either are the same :P)