Friendly reminder that this doesn't exactly give you buy two get one free, it just drops the price of each by whichever the lowest-price game would be.
So if you bought three $60 games, they'd all be discounted to $40. So if you want to just get 1-2 games, you could always buy a third game you don't want, then return it, and you still get two games for $80.
Also, yeah, don't expect first-party Switch to be included in this outside of some limited titles. One year I got lucky because the special edition of Splatoon 2 (the one with the booklet) was apparently forgotten to be excluded, and I was able to grab it. But yeah, if you're looking to score Mario 3D World in this, not gonna happen.