Sugar is one of the two tertiary antagonists of the movie Batman Forever, and one of Two-Face's love interests (and eventually the Riddler's minion), the other being Spice. She is played by Drew Barrymore.
Sugar is sweetness and light, and about as good as the good side of what Two-Face deserves. She is the exact opposite of Spice.
Near the end of the film, Sugar and the Riddler began a romantic relationship together. They discovered Batman's secret identity. She also helped him into his trap for the Dark Knight.
Not much is known about Sugar. Her real name is unknown, and she doesn't have an established backstory and it is unknown how she met Two-Face. It is also unknown what became of her after Two-Face's death, though it is likely she changed her ways or left Gotham before she gets arrested.