For example, if you create a gaming mouse, buy ten retail copies of the new Doom 7 right off the retail shelves and offer them for promotional purposes at no cost along with your mouse, the publisher (or sometimes game creator) can ask you to cease and desist. The lawsuit, were one to occur, might argue that you're causing misrepresentation (have to be careful not to make it look like your gaming mouse is being endorsed by the game creator or publisher etc), or claim that you're damaging their game's brand through commercial association they didn't approve of, and they could also go the route of claiming you're commercially benefiting from association with their game / brand and seek monetary compensation.

Way back when, circa mid to late 1990's I ran into these types of problems in the gaming industry with a company I operated. The gaming world was a lot more legally benign back then and it was still a serious problem. Back then you could often easily get permission from the company to do a promotion, but you properly would check in with their PR / marketing group and get formal approval. id Software was often decent about these types of things. They did a zillion community promotions of all sorts.