If Gendry had access to the physgun from Garry's mod, he would have incredible control over objects and people through a telekinetic-like power. He could easily lift heavy objects and throw them with ease. He could also move people around and even manipulate their bodies, potentially making him a powerful warrior. However, if this power fell into the wrong hands, it could become dangerous and destructive. Ultimately, the addition of the physgun to Gendry's arsenal would significantly change his character and impact the overall storyline of Game of Thrones.

It would be challenging to explain the physgun from Garry's mod in the Game of Thrones universe, as it is a highly advanced technological tool that seems out of place in the fantasy world of Westeros. One possible explanation could be that the physgun is a mystical artifact, possessed by a powerful wizard or sorcerer who traveled from another world or time. Alternatively, it could be a product of ancient Valyrian technology, developed during a time when magic was more prevalent in the world. Another possibility is that it was created by the Children of the Forest, who were known to have powerful magic at their disposal. However, no matter the explanation, the physgun would undoubtedly be a game-changer in the battles fought in the Seven Kingdoms.