Kill in no set order:
In the same order, they drop the following seven Gems that you will need to obtain.
You'll probably need to do this multiple times to obtain the gems from them. Locker them so you don't use them as astral reagents. Once you have all seven journey to the bottom of Hellbent Mountain and visit the monk in the galaxy of stars. Walk into the room with all the gems in your inventory. The monk will ask you pick a power from the a list:
Say which you choose and you will be awarded the mark, and an orb of powers.