You will bump into the Crippled Rhogar immediately after killing the Infiltrator boss. This fellow will give you a side-quest to hunt down the Human Skull collectible items that can be found in the Keystone Crypt, Catacombs and Keystone Citadel. He will offer a reward for bringing them to him.
Upon leaving the Rhogar realm and returning, he will have moved to a snowy ledge overlooking a cliff in the Abandoned Field area by the back entrance to the main Temple (where we entered to fight the Infiltrator).
There are 30 Human Skulls in total (5 in the Keystone Crypt/Graveyard, 21 in the Catacombs and 4 in Keystone Citadel) and if you follow the guide you should be able to find them all by the time you reach him on your second visit to the Rhogar realm. There are a couple of rewards on offer for handing in Human Skulls and they include:
- 15 Human Skulls – Shield (Stance) + 2,000 XP
30 Human Skulls – Trinket (Leech) + 2,000 XP.
Note that upon handing in all 30 Human Skulls , the quest giver will summon a pair of Rhogar Knights and a Spellcaster to attack you. As such, make sure you are prepared for a fight before you speak with him! Once you have dealt with the enemies, kill the quest giver for the 30 skull reward.