Hello, I wanted an explanation, I always use the assets purchased under license, But I have a friend who almost always uses assets for free, which in this case are not free, on pirate websites, I wanted to know what happens if he uses these assets in your game for marketing?
i imagine that if your friend is using pirated (stolen) assets then it would be just like using anything fraudulent. if found out i’m sure there would be some kind of legal action taken against them (cease and desist, forfeiture of profit, etc).
theres plenty of legitimate places to get free assets and if your looking to publish a game and make money from it then its worth the investment to buy the assets.
do note that this is just my opinion, i am not a lawyer, and i do not work for epic.
“I have a friend who…” lol 
I am not a lawyer either, but I would like to put more emphasis on the fact that using pirated assets means using them without a license, the repercussions for this depend on where your friend lives (the laws that would apply) and whether the creator or authorities notice this.
From a marketing point of view, if someone notices and calls him out on this, his project will look like a scam. So… 0/10 would not recommend.
However, if he is using these pirated assets in videos/pictures only (he is not distributing their assets, only showing depictions of them), if the creators are mentioned, and the assets are bought before the product is released, maybe he could ask the creators of the assets for permission to use the assets in derivative works (video/pictures), before buying them. If they say yes, he could do that. And only that. Don’t release a game with unlicensed content.
Also: This is not legal advice. If you want legal advice, you have to ask a lawyer.
You should be really careful with pirated assets not only meshes even code as well, look at West Wolrd app game they used some old code from Bethesda Fallout Shelter on their game and had their game completely removed and most likely paid few huge fines as well.
If you are not sure if the asset is pirated or not do not use it, most free assets come with a letter of use (forgot how it called) where it’s written if you can use the asset commercially or if you need to give credit to the creator etc.
In most cases, if you just building a fan-based game and not getting money out of it you and stay under the radar nothing will happen, but there are cases like with Nintendo that had few fan-based games removed, so if you think using pirated assets think of the risks(again not a lawyer but knowledge that gathered from here and there).