I don't see the need for pets at the moment in PL. But if we were to have them I guess the best bet would have them to be like "spirits" like well in RPG they will be like "Inner Animal Spirits" or The "spirits of our animal ancestors". They will be in game mostly be like glowing small orbs but in game they will have a purpose. Some orbs (spirits) will boost our health/mana/etc. Others will actually help or shield you in battle. Also another good thing if we did do this would be being able to bye upgrades for the orbs (spirits) to better attack our enemies or better boost our health/mana or even better shield us from attacks. The whole scenario of the "inner animal spirit" or "spirits of our animal ancestors" would definitely help not only in lore and story but probably add more quests!