Can I sell my asset with Unity art?

I am putting together an asset for the Asset store. My asset currently uses my programmer art, and it is terrible. Can I use free assets published by Unity Technologies, such as their 2D Pack, as the art in my asset?

Not a lawyer answer. Yes. But exact terms depend on each individual “asset”'s license. “Free” is ambiguous and almost always isn’t actually free free, as in, public domain or CC0. (Price is irrelevant.) In this case, you should follow the “View License Agreement” link on the Asset store. Most importantly, licenses such as this Apache 2.0 require you to include attribution in your work – usually, the same license. See the “4. Redistribution.” section. In short, you can use it, as long as you include the license. In you modify, you can change the license, but you still need attribute. It gets muddy with exact details and no one is really too anal about it, but something to keep in mind.