What do I do with this poor baby?

[hollowlaughter]

You need to feed live then. I am sorry but it is more often than not that a new owner gets a ball python without any idea of the previous feeding habits. At least you know it was feeding live. You are going to have to do that for a while until you get it settled in and growing.

I recommend finding a pet store that offers fuzzy or hopper mice and purchase those. It is often very difficult to get a ball python swapped to frozen thawed rodents when you are also trying to correct husbandry issues and get them acclimated. It would be far better to feed the same prey type the breeder or seller was doing. Pinky mice are almost all gelatinous cartilage and fat and not really nutritious toward larger juvenile snakes like ball pythons. Starting on fuzzy or weaned mice would be far more nutritious and finding a smaller hopper mouse would be best.

Get him feeding then worry about switching to frozen thawed.

They mentioned that their local pet stores aren't carrying live, they may be in one of the states/countries with a live feeder ban, which I'd point to as a breeder-based issue. Hindsight's 20/20, not everyone goes into it knowing to look for an animal already established on f/t rats.

Otherwise, correct. Upgrading this animal over time (aka pinky mice > fuzzy mice > hopper mice > etc) will probably be best to not stress its digestive system with a large jump in prey size, especially if it's already malnourished from its time in the breeder's care. Here's a recent guide on that. It'll be easier to swap once the animal is an established eater so you can afford to have it fast for a few months as it tries to wait you out for another mouse.