Frisk has red-brown hair, a huge body like Asgore and two horns. One is smaller than the other one and they always wears a crown.
Frisk is a heartless human-creature who always does always what they want. Frisk seems totally like the natural dark lord.
Frisk proved that they really hated Toriel and long letters about love and peace and Asgore, however, it showed a romantic interest to her that he said: " if she didn't get mama word wrong maybe she could get a chance with me ."
"So what's left for you, no family, no friends, no home. Nothing. run away and show me what you will do."
– Frisk talking with Sans.
Frisk appears that they have fun to pick on Sans and his weaknesses to the extent his the only one alive only to see what he will do.