Looking at the black substance that substituted as blood, Aiden thought back to the illusion. The quest he received from the system said that he had to banish and cleanse the Nightmare, this unknown entity that corrupted their host's minds.
Every time he banished one, and as their hosts overcame their clouded thoughts, feelings, or died in the case of the terrorists, a similar substance evaporated into the air. It was only for a fragment of a moment, but Aiden still managed to catch the sight several times.
While not completely the same, the feeling he got from looking at the oozing thick black substance was the same.
'So, he is also affected by the Nightmare… Their influence on him is probably higher than in the previous cases. Hmm…' Aiden was thinking to himself.