Delve Too Deep: Sefina Rousseau

This is what I would consider an explorer/support style Sefina. You have plenty of ways to get yourself out of trouble, such as Elusive and Ward of Protection. Coupled with your naturally high agility and willpower, you should be fairly competent at getting out of sticky situations alive.

Until you get Shrivelling, Rite of Seeking, or a Flashlight (which shouldn't be too hard given your enormous starting hand), you're not going to be particularly competent at helping out. Thus, get out there and start uncovering as much of the map as possible as quickly as you can. Not only is this an essential part of most missions, but it'll help your allies avoid any nasty traps that may spring up on entering certain locations.

Other than that, you don't have any specific playstyle. Do your best to support your allies, possibly by even simply engaging and evading enemies. Once you've done your lap of the map, it's best to stick with your allies to provide aid as quickly as you can.

When levelling up, there are plenty of great options for you to take. If you're confident, the first thing to purchase is  Charon's Obol. At the moment, this amounts to +10XP over the course of the campaign, so long as you're not ever defeated. Coupled with Delve Too Deep, this can provide you with absurd amounts of XP. Just don't say I didn't warn you about being careful, okay?

Fortunately, you're one of the best investigators at staying alive, so Charon's Obol is less risky for you. Of course, you can also Cheat Death once you're experienced enough, or simply talk your way out of things with Suggestion. Streetwise can you out with both survival and investigation, especially if you're on a Hot Streak.

Sneak Attack (Level 2) and Ward of Protection (Level 2) are great additions, allowing you to improve your supportive abilities greatly. The very funky Time Warp is yet another unique card that is particularly suited to Sefina. You'll be able to do alter time more than any other investigator, thanks to The Painted World!

Cut Backstab to make room for Sneak Attack (Level 2), Emergency Cache for Hot Streak, and your choice of utility events for Time Warp and Cheat Death (if you decide to go for it). Delve Too Deep can be cut later in the campaign given how dangerous it can become, allowing you to make room for some of your more powerful tricks. After all, the goal is to beat the campaign, not grab the most XP!