And also how do you make your HA zombie?

You can make your pet Galactic by visiting the Coda caves on the 7th and 8th of every month.

The Zombie event was in February, it's currently not possible to make your HA a zombie. Sorry!

you can't become a zombie anymore, the event is over.

To make a galactic pet, you need to visit the Coda Caves (open on the 7th and 8th of every month). You will have to hand in some gems, and then your pet can be made galactic :)