Satan - also known as DEVIL. She is the personification of EVIL and a figure of TEMPTATION. Her bad Temper, Cruelty and Wickedness are so extreme to evoke a personality of DEVIL/ EVIL in herself.
HORNS on her forehead represents Victorious Strength - Source of her Power. Blood dripping down is symbolic to Growth of Horns - the larger it Grows, the more Powerful her ability becomes.
FLYING BAT EYES allows her to be in total control of her surroundings. She is capable of manipulating other to see what she wishes them to see.

While I believe GOOD and EVIL is common Dichotomy. Everyone is prone to behave like an EVIL Incarnate under the influence of situational forces.
"It is just a matter of choice - EVIL OR GOOD
"Monsters are Real, Ghosts are Real too. They Live inside us and sometimes they Win" - Stephen King.