Hocus Pocus

In 1693, Salem, Massachusetts, during the Salem witch trials, Thackery Binx sees his little sister, Emily, spirited away to the cottage of three witches. There, the Sanderson sisters, Winifred, Sarah and Mary, cast a spell on Emily to absorb her youth and regain their own, killing her in the process. Binx confronts the witches who transform him into an immortal black cat to live with his guilt at not saving Emily. The townsfolk, led by Binx's father, capture and hang the witches, but Winifred's spellbook casts a curse that will resurrect the witches on All Hallows Eve when any virgin lights the Black Flame Candle. Binx guards the cottage to ensure no one summons the witches.
300 years later in 1993, Max Dennison moves from Los Angeles to Salem with his family, including his sister Dani. While exploring the town, he and Dani meet Allison, whose family owns the Sanderson cottage as a museum. Max suggests that they go there and impress Allison, but promised Dani to go trick-or-treating.
Investigating inside the cottage, Max lights the Black Flame Candle and inadvertently resurrects the witches, who plot to continue their plan to suck out the souls of all of Salem's children, beginning with Dani. The children escape, while Max steals Winifred's spell book on advice from the Binx. The witches pursue them to a cemetery, where Winifred raises her unfaithful lover Billy Butcherson as a zombie to chase them on foot. The witches try to acclimate to the 20th century, but are horrified when they discover Halloween and their broomsticks are stolen by three girls. The witches plan to achieve their goals or else they will be disintegrated on sunrise. They pursue the children across town using Mary's enhanced sense of smell. Max, Allison and Dani find their parents at a Halloween party at the town hall, where Winifred enchants the partygoers to dance and sing. At Jacob Bailey High School, the children trap the witches in a kiln to burn them alive. While the children celebrates, the witches' curse revives them, and they kidnap Dani and Binx after Max and Allison open the spellbook. Sarah then uses her siren-like voice to mesmerize Salem's children and lure them to the Sandersons' cottage. Max and Allison rescue Dani and Binx by tricking the witches into believing sunrise came an hour early.
Back at the cemetery, Max runs into Billy, who cuts open his stitched up mouth and insults Winifred, joining Max to protect Dani. The witches attack and Winifred attempts to suck out the soul from Dani with the single vial of potion she retrieved from her cauldron. Binx leaps on Winifred and knocks the potion out of her hand into Max's, but Binx is thrown to the ground and mortally wounded. Rather than smashing the vial, Max drinks it and apparently makes himself a sacrifice. As the sun rises, Winifred fails to suck out the soul from Max after falling into the hallowed ground, and Winifred is petrified and disintegrated along with her sisters.
As the satisfied Billy returns to his grave, Binx dies freeing his soul, thanking Max, Dani and Allison for help, and bids farewell to them, before he and Emily walk into the afterlife. During the end credits, the exhausted partygoers are freed from the spell and return home. Back at the cottage, Winifred's spellbook opens its eye to seek its master and hints that the Sanderson sisters might return again.

Question: Who joins Max to protect Dani?
Answer: Billy