From Walmart. Never had one. I use a Pizzazz pizza cooker (the turntable thing), so I took the pizza out of the box, took off the plastic, and lifted it out of the black tray it was in. I was startled to find the bottom of the pizza slimy wet. It wasn’t water because the pizza was frozen solid, so I’m guessing it was vegetable oil. Much later, I read the instructions on the box which said to bake it in that black tray. I’ve never seen a frozen pizza like that. Is it a new thing 
Not new in my experience. I’ve purchased grocery pizzas that have that black cooking tray. It’s supposed to help with crisping of the pizza crust. I don’t usually bother with it because I prefer to just put the pizza down on a preheated pizza stone.
How was that WalMart pizza compared to chain delivery or some other frozen name brand?
Well, this is the first I’ve heard of it. All my frozen pizzas are plastic wrapped and usually sitting atop a circle of cardboard. No idea what this black tray is.
It was alright, but might have been better had I followed instructions and baked it in the oven on the black tray. I’ll buy another and try someday.
Dominic’s in store pizzas from the deli came with one. As noted it’s supposed to help cook the crust. As far as grocery store take-n-bake goes they didn’t completely suck, which I realize is faint praise.