Opening scene would focus on two people wandering through a museum, looking at the exhibits and talking. These are the two main characters, and like I said before, I don't have much worked out about these people. One of them's a thinker, capable of working out what the hell's going when shit hits the fan in the future, while the others an athletic-type, good for the various action-movie maneuvers that will be needed. This opening scene establishes these two, their personality's, an big fancy recently unveiled ancient egypt exhibit, and a reason that they'll both be at the museum after dark, which sets up the next scene.
The next scene is them after-dark at the museum, things are normal, and the two are doing whatever they were here to do, when a guard examining the Egypt gets killed. The moment someone realizes "Hey, where did Frank go?" is when the Mummy is fully unleashed from their Sarcophagus within the Egypt exhibit. The Thinker and Athlete pair barely escape with their lives, while everyone else at the museum at that is killed.
I don't have the rest of the movie's plot worked out, but the duo would find themselves trying to keep an artifact away from the Mummy, because if the Mummy gets this artifact then it will obtain god-like powers, and be capable of realizing whatever evil desires it has in mind. However, after chasing the duo through whatever city the action takes place in (Probably New York) and back to the museum, the Mummy finally manages to claim the artifact from the duo.
Things now looking completely doomed, the athlete character charges the Mummy in a desperate attempt to buy the Thinker character a few seconds to get away alive, but is effortlessly backhanded into another exhibit. This exhibit would have been shown earlier, but it would have to be shown carefully, so that the audience doesn't immediately realize what's up.
The Exhibit in question is about the origins of Rome, including it's mythological Founders Romulus and Remus, who were (At least a little-bit) raised by a wolf.
This is going exactly where you think it's going.
As the Mummy stalks towards the Thinker character, the Athlete sits up, pulls a large fang that was part of the exhibit out of their arm, says something along the lines of "I don't feel so good..." and then, in a single glorious 360-degree angle shot, transforms into a werewolf. (This would be the 'audience loses their shit' part of the film, as an aside).
And so, after a pitched battle between the Mummy and the Athlete-turned Werewolf, the Werewolf finally pounds the Mummy into dust, then holds back it's rage enough to not then turn on the thinker character, instead running from the scene. The final shot of the movie (After a brief 'Where are they now?" with the Thinker) is the Werewolf silhouetted against the moon, roaring up into the night sky.
The mid-credits would show the outside of the museum in chaos as a result of the Mummies brief godhood and subsequent battle with a Werewolf, with police and other emergency services running. The camera would focus on one random citizen observing the action, trying to work out what's going on, before finding a ancient piece of jewelry on the ground. Their face is turned away from the camera as they reach down to pick it up, until someone starts talking to them. The citizen finally turns towards the camera and starts talking, but the way in comparison to before they picked up the jewelry all-but tells the audience that the somehow still alive Mummy has taken control of this person.
