Strength is an essential stat in the game of Powerpets, both in order to qualify for Supreme Elite status and in order to have an effective pet in the Powerdome, where pets can fight other pets or certain characters in the game world. Strength is also needed to increase the amount of armour your pet can have when armouring at the Armory, located in North New Barkston.
In order to increase strength, players can feed their pets slime or have them eat or play with radioactive items. Slime can be picked up in the Northern Woods in North New Barkston or purified from the Slime Purifier in Mini City; radioactive items can be bought from players, shops or won from different quests and games. However, be aware that the effect of slime and radioactive items on increasing a Pet's Strength can only go so far. In order to further enhance a pet's strength, players will eventually have to use the Berry Box and feed pets items that are obtained from there.