Have at least 1 pet with an overall rating of 100 or more

I dont get it

Your pet's stats need to add up to 100+, only Health, Level, Defense and Strength count

it's not well explained there is it?

Here's a quote from Frequently Asked Questions & Answers stickied in this very subforum:

What does that mean by Have at least 1 pet with an overall rating of 100 or more?

It means that you must have a pet that has 100 or more in it`s Level, Health, Defense or Strength stats. It can be either one of those, or combined. Intelligence and Speed are not included in the overall rating though.

Example: If your pet has stats of Level: 1, Strength: 10, Defense: 10, Health: 10, then its overall rating is: 1 + 10 + 10 + 10 = 31.