Tegan leaves part way through the twenty-first season. Her player hasn't quite given up on the idea of playing a colonial, instead of yet another Brit, but evidently feels that her next character should do a lot more screaming and a lot less of anything useful, bringing back some of the flavour of the campaign's early days.
The result, on the basis of what someone has assured her is an entirely typical name in the US, is American college student Perpugilliam "Peri" Brown.
In the actual show, Peri's primary functions are to look pretty and scream at the monsters. Neither, it has to be said, is a really sound basis for a player character. Indeed, with the recent departure of Turlough, we're back once again to the "Doctor plus one female companion" model, which also doesn't fit wel with the metaphor of an RPG. It's a model that the show will stick with, more or less, from here on in, but for our purposes, we're going to brush that aside and try to look at Peri as she might fit into a more typical group.
This isn't easy, not least because if the writers had any clear concept of her personality traits beyond "she's American", they made a poor job of fleshing them out. Granted, this is more of a concept than they had with Dodo, but that's damning with faint praise.
To be honest, Peri isn't a very proactive character, and she's often getting lost (she certainly doesn't have Sense of Direction), getting captured, failing to run away from things, and so on. Presumably, she's gaining Story Points from this, retreading the 'Peril Monkey' role of '60s companions like Victoria. To make her more than that we have to, as we did with some of those characters, look at what she's supposed to be good at, rather than what skills she effectively demonstrates on screen.