With the Siege of the Atlas expansion opening the door to more than a few new options for Path of Exile players, from Omniscience to new Eldritch Currency, it would be easy to miss a few. But whatever you do, don’t overlook Forbidden Flesh and Forbidden Flame, which introduce one of the more exciting new mechanics to the game.

These two new unique gems give players the ability to gain skills from different Ascendancy classes, something we’ve never been able to do before in Path of Exile. The process isn’t as easy as simply finding the gems and equipping them, though.

The first trick to unlocking the power of these gems is finding them. And although it won’t be easy, this part is at least straightforward. The gems will drop from the two new Pinnacle bosses added in the Siege of the Atlas expansion. Forbidden Flesh can drop from The Eater of Worlds, while Forbidden Flame can drop from The Searing Exarch.

But getting both halves isn’t enough. You will also need to make sure the halves have matching Ascendancy Passives. And while they can be from a different Ascendancy class than your character, they will still need to match your overarching class. So for instance, a Champion could gain skills from the Slayer or Gladiator Passive trees, but not from the Elementalist Passive tree.