A hydraulic fracking plug assembly comprises a mandrel, sealing element, upper and lower backup rings, upper and lower cones, upper and lower slips each having teeth configured to engage a well casing, and a shoe. At least one of these parts, and in a further example most or all of these parts, are soluble in a solvent such as a potassium chloride solution, an acid, or a base. In some such examples, the soluble parts comprise magnesium, a magnesium alloy, or a soluble polymer.