I've been playing a bunch of the base pack since the update dropped in order to finish off some of the achievements I was missing, like the Level 3 Rat, Whale, and Chick. The balance changes are a mixed bag- they definitely toned down some things in reasonable ways, like the Ox, Penguin, and Bison, but the Crab is just unviable now which is pretty lame to me. I'm loving what they did with the Squirrel, especially given that food-based scaling teams are stronger than ever with the Cat somehow still not getting nerfed at all. The Worm is thriving in this meta as a recipient of broken food teams, but another cool one that's standing out for me is the buffed Peacock paired with Rabbit in order to let it just run through teams in the early-to-mid game with a massive health pool and garlic armor. I haven't played a whole lot of the new stuff yet but I despise the Vulture with a passion.
Oh also if anyone wants to make a tier list for pets, I dug through tiermaker.com and found this complete template!
