Voice Description*: Nightmare isn't necessarily the most popular of alternate sanses, but I will try my best to give a description regardless. I imagine his voice to be deep and mildly unsettling. He is a very cunning character who feeds off of negativity and does what he wants, when he wants. 

Various interpretations of his voice can be found through fandubs, I highly suggest using them as reference!

*Note: Like all voiceless characters, this is up to interpretation. If you have your own interpretation of this character's voice, by all means try it!

Personality from UT Fanon AU

Personality: 

He's deceiving, erratic, and unpredictable. He sees everyone's as mere tools to further his goals and is completely devoid of empathy. He's also Intelligent, and often comes up with countless schemes to bring absolute suffering to existence. He's filled with pure and utter hatred, wanting everyone to be in a perpetual state of torment.