The Doctor (10) and the Rain (2)

Now that she's traveling with another Doctor, who has never had any companions, her regenerations start turning her into the parallel versions of Martha (2), Donna (3), and Rose (5). Martha Jones, Donna Noble, and Rose Tyler don't exist in this parallel world. Although, for some odd reason, she has strange tattoos below her eyes. This helps identify who is who when she returns to help the original Doctor in "Journey's End."