To Summon Pets, you need to have the Pet Whistles which can be obtained while Run or can be bought in the Shop.
While running, if you need to summon your chosen Pet, tap the screen twice and enjoy the wonderful ride, which can even save you to lose the game once and boost your score for a limited time.
Pets have their special powers, they shoot, which makes them able to attack Monsters from a distance, they can also act as magnets and will attract all the Coins present till the limited time.