Observations about the teaser
At about 0:08, just before the shot of Tom Cruise under water, there's another shot (presumably from the same scene) of a few submerged sarcophagi. Look to the right, however: one of them is opened up, and what looks like another mummy, or some other sort of undead fellow, is rising up out of it.
At about 0:10, if you pause it over the shot of the titular Mummy in silhouette, some more things are noticeable. One, she's holding a dagger in her right hand. Two, she's in some large ruins, which curiously look more Roman than anything near Egypt. There's also what looks like a bunch more mummies or undead people. Could she be raising an army? What's also curious about this shot is that it seems she's walking into these ruins from within a modern structure, based on what looks like doors that are being opened as she walks out.
The very next shot is of Russell Crowe as Dr. Jekyll, for those of you who didn't notice him.
I may update this if I notice anything else, though there's probably not much left in the teaser itself. We'll have to wait for the full trailer.
<i>Warning! The Monster is loose!</I>