With the 8.0 update many things about pets have changed. Firstly the pet album has been added. This is a place were you can collect specific pets into collections to unlock stars and gain the corresponding bonus. As you unlock stars more collections become available. Second, almost every pet is now attainable in the normal summon including the best pet in the game many say, the air spirit. There has been debate that they changed him because his ability now reads crit chance. As a user of the air spirit I can squash that for everyone, it still affects crit damage. They may have wanted to change him and may still in the future, but all they changed was the description. Though the air spirit is the best as far as an elite gamer is concerned there are many cool pets and useful ones now that you can use, it's really on your preference.