Pet Battle Bonus Event (September 23 – 28)

The Pet Battle Bonus Event runs from September 23rd through 28th and is a great time to level pets. During this event, you will get the Sign of the Critter which increases experience gained by pets by 200%. This should help a lot with getting a crew of pets up to 25.
More you can read here: Pet Battle Bonus Event (September 23 – 28).