Overview:

tldr: This is a deck designed for a pacifist run. Evade enemies, find clues, get the hell out.

Sefina's ability lets her play a single event up to 5 times per scenario. This lets her get a lot more mileage out of the strong events in her deck. She draws 13 cards at the start of each scenario, making her the most reliable investigator for finding important pieces like De Luca and Lone Wolf turn 1.

Sefina's base stats in fight and intellect are terrible. You never want to do either. Instead, with the Rogue and Mystic cards, and her triple unique, Sefina is well-situated to do pacifist runs at high difficulty. She's good at evasion, and has decent willpower for dealing with Treacheries Her card pool gives her a lot of options to deal with enemies without having to fight them, and to get clues without intellect checks.

I've played this deck through on Standard, and am in the middle of a hard campaign. The play style is a lot of fun. When things go smoothly, she coasts through each scenario. If enemies start to pile up, you end up with very little room for error, and may end up having to resign or die.

Enemies: I personally prefer the harrowing experience of scrabbling for clues as the enemies begin to fill up the board. Fighting enemies takes up valuable actions, resources, and cards. This deck is built to avoid that hassle. Try to evade enemies, and then move away.

Hunters are problematic, since they will continue to cost you in health, actions, and resources/cards for evade checks. Some non-hunter enemies sit on central locations that you need to pass through frequently. If you don't want to play full pacifist, you can slot Backstab and Shrivelling to deal with them. If you run Rite + Shrivelling, Holy Rosary and Uncage the Soul are good support cards.

Clues: When playing this deck, you need to find clues fast. Move quickly so you can finish the scenario before too many monsters spawn. As time progresses, the locations will become too monster dense, and you won't have enough actions to move or investigate safely. The MVP of the deck is Drawn to the Flame - 2 clues for one action and no skill check. Use The Painted World to spam it out. Flashlight is for investigating 1 or 2 shroud locations. Rite of Seeking gives an extra clue, which is a lifesaver when tight on actions. Double or Nothing combos with Rite and Flashlight for action compression.

Actions: Fortunately, these are a Rogue specialty. A turn one Leo De Luca is a game changer. At later levels, add in a Ace in the Hole.

Staying out of trouble: When you move to a location, plan to get all the clues before the end of your turn. Otherwise, you might spawn enemies before you finish there. Elusive and Think on Your Feet are great for evading evade checks. Don't let enemies pile up. When things get hot, don't be afraid to get the hell out. (Fun fact and spoiler: you can resign from almost all the scenarios in the Dunwich campaign)

Resources are tight, especially once you start using Streetwise and Lucky Dice. Lone Wolf is amazing at low player counts. Getting Hot Streak asap will alleviate any money problems.

Upgrades:

Delve Too Deep will make up for the XP you miss from not killing enemies. Prioritize finding both Delves and investigating Victory locations to maximize XP.

Hot Streak If you draw this in your opening hand, you can make a fortune off it using The Painted World

Lockpicks give you another clue finding tool. Best for high shroud, low clue count locations. Better at low player counts, since it can only be used once per turn.

Streetwise. Permanents are good. Gives an intellect boost option.

Moxie Pay to boost can help pass impossible checks. Has the perfect icons. Synergizes with Holy Rosary

Lucky Dice Once you get money, these dice are amazing.

Ace in the Hole. 3 bonus actions? Hell yeah. Actions are really tight when playing for evasion. When enemies start to pile up, this card can save your life.

Cat Burglar is good to deal with non-hunters, especially ones with high evade. The passive agility is great too. Ally slots are tight. Using this means also adding Charisma.

Upgraded Emergency Cache is alright if you have a lot of extra XP.

Flex cards: Stealth is situational. Lowering the evade check is very useful. However, the enemy will re-engage you at the end of your turn, unless you move away. For hunters, it's better to evade them normally so they don't follow you. Near the end of the campaign, enemies tend to have higher evade values, so Stealth won't give you a guaranteed success.

Holy Rosary should be replaced when you get Lucky Dice, since they fill the same slot.

Fine Clothes can be situationally useful. More valuable when replaying the campaign.

Painkillers can balance your health pool, if you're having difficulty with the low hp.

Uncage the Soul is a better emergency cache. It saves an action, and has 2 willpower. I wouldn't use it unless I also added Shrivelling.

Upgraded Pickpocketing is much better than the level 0. It's fast, gives card draw, and has better icons. It combos with Stealth, but not Elusive or Cat Burglar.