The revival potion has the power the bring the dead back to life, but can't revive their original souls. Benny's Grandma kept this potion on a secret shelf, possibly as a precautionary measure to keep it away from Benny. Any more than a few drops can cause major disaster.
In Lawn of the Dead, Benny stole the potion to revive the dead Puffles in order to win Della's heart, but created a disaster. When the potion was spread to many animals' dead bodies, they were reanimated and began to attack the town.
An Anti-Revival potion reverses the effects of the revival potion and incinerates the reanimated bodies. Ethan, Benny and Sarah are charged with the task of turning the demon animals back with this potion.