Box with Mug Mockup
The best Mug Mockup will make your designs look realistic. Then, use the smart object layer where you can integrate your designs easily. You may also upload your designs on the visible sides of the box.
Free

The best Mug Mockup you can do product brandings or prompt your brand name. This free mockup is a set of two coffee mugs that can be easily branded via smart objects, you can also customize the color of mugs from inside and outside.