Power

His back was drenched in sweat because of the pressure he felt from the two beings in front of him. His body was shaking in fear. He tried to get a good look at both of them as they floated in the distance. 

By one glance he understood they weren't human. They had horns on their forehead. The one on the right had two while the left one had only one. Both of their bodies were purple with lines on them which seemed like cracks, giving out an eerie feeling. The black miasma oozing out of them was the reason for the uneasiness Mark felt. 

Both of them continued to get near as the pressure he felt grew. They stopped a foot away from him and the pressure was too much for him to handle. If he was not forcing himself, then he would have fainted. He was on a very thin thread, hoping that they wouldn't increase the pressure he was already facing.