Congratz! Its always nice to hit milestones ^_^
Dont stop collecting tho, you know its just a matter of time before there will be an achievement for x00 pets
400 is a nice milestone to hit, enjoy your new pets and good luck getting to the 500 mark.
"Even when you are winning soundly, you must always give your opponent a way to retreat with honor. If you don't, then he has no reason to surrender. He will fight until the bitter end, and you will pay a larger price for victory."