Fear

It was pretty convenient that Nightingale stopped being a bother. 

The Royal Nightshadow Elf was much easier to deal with and so was the Nightshadow Elven cohort around him.

They obeyed the commands of the Royal Nightshadow Elf, who in turn obeyed Nial. Thus, one could say that Nial had everything under control.

'Sometimes it feels great to possess the Essence of Darkness. It's like having another race in my grasp.'

Looking around at the ravine, Nial walked slowly and unhurriedly toward one end of it. It looked like there was nothing special in that direction but Nial knew better.

He might not be able to see something but his range of perception, combined with his Mana Sense were strong enough to perceive the 'lack of mana' in certain areas around this side of the ravine.