Halloween Witches Brew Green Slime Drink Mix in Cauldron According to Target, if you mix the drink powder with tonic water the green slime will glow under a blacklight. When mixed, the powder and tonic water form a thick bubbling Halloween Witches Brew Green Slime Drink Mix in Cauldron ($8). Image Source: target.com Halloween Witches Brew Green Slime Drink Mix in Cauldron $8 from target.com Buy Now