How do you use it, and can it cause ALL your pets to mutate? I'm thinking about purchasing one, but I don't want to risk my more costly colored pets...

You have to feed it to your pet like any other item, but all it does is fill hunger. It won't keep your pet fed. It doesn't actually mutate your pets, but it is far more expensive than just sticking them in the Resort or Rathskeller Inn

What a sadly misleading item. Thanks for letting me know! I'll stick with the resort then.

Although, what is the Rathskeller Inn? Is it something new on the site? I don't remember seeing it.

Definitely not new. It's in the Omen Islands, and it's a restocking shop (that's where Babette, the pirate mommy works) but in the text underneath her picture there's a link to the Inn. You have to add your pets one at a time, with or without a GA, but iirc it costs the same and you can put your pets in for one week longer

Ahhh! I see! Cool. I had no idea. After my pets are out of the resort I'll start using the inn c= Thanks!

the Rathskellar Inn didn't used to have it's own map link in Pirate Cove, but now it does. It's above the Rathskellar Shop (which got renamed at the same time). Both of these things happened during the last Site Event in which Merana our dark mistress was finally freed.

The Infinity Berry is useful for when the hunger coding in Subeta fails, as it feeds your pet full up. This way you can keep on fighting without feeding your pet foods one-by-one or making sure that you are only going into quickfights.

I use it all the time, and alas, no mutations at all.

Also good to know!