Yep, IIRC that’s the purple/purple ones, do battles in Karakoth - challenges are easiest - also set it as your home kingdom so your revenge battles are here.
Arcane drop rates are very low though… get ready for a good ol’ grind… suggest run a soul farm team so you benefit from the time spent… Here’s a great thread: Gems of Farmville - #32 by turintuor