Counterspell Diana Delves Too Deep

Diana Stanley starts with very low willpower and otherwise capable but not outstanding stats. Her power makes several otherwise lackluster cards into cheaper (or resource generating) cantrips. I think that this favors building based around her strength and intellect, and using her willpower mainly for upgraded spells. The best of the “counterspells” (ignore/cancel cards) can only be played in response to an attack or treachery card, so Delve Too Deep and Drawn to the Flame can be used when you have extra counterspells, to keep the engine going.

Combat: Machete, tutored with Prepared for the Worst and backed with Beat Cop and Vicious Blow. Storm of Spirits covers Machete's weakness in crowd control, and can be powered up with Take the Initiative or Steadfast if needed early when Diana’s will is weak. Twilight Blade helps with odd health enemies in the late game and gives great card advantage by reusing counterspells and opening up space for her activated power again. Relying heavily on Machete should work in this deck, since the deck cycles quickly and you can protect the Machete from treachery effects with your counterspells. I think the standard mystic spells (e.g. Shrivelling) are just too weak here since Diana starts with such low willpower.

Investigating: With 3 intellect, Flashlight and Perception are pretty reliable. Drawn to the Flame can be used for high shroud locations at opportune moments.

Other assets: Holy Rosary adds too little willpower in the early game, and is not needed in the late game, restricting its use. Physical Training is not included because the deck does not have strong resource generation.

"Counterspells" included:

1. Dark Prophecy: not very strong, but super easy to use and Diana Stanley’s power completely refunds its cost, thus thinning out your deck. Will be switched out for better upgrade counterspells later.
2. Deny Existence, Delay the Inevitable, Dodge, and Hypnotic Gaze: These cards require a specific situation to be used (enemy attack, damage or horror, etc), so may sit in your hand for some time before being used. If you don’t draw Machete, these cards help you survive AND draw! If you are desperate for cards, you can draw a card, cancel the attack of opportunity with one of your counterspells, and get a free draw from Diana Stanley's power! If you do have your Machete, Delve too Deep and Drawn to the Flame can increase the challenge and make the above cards more useful.
3. Ward of Protection: This card is commonly used in many decks and is an obvious inclusion here.

Not included:

1. Eldritch Inspiration: too situational.
2. Defiance: rarely ignores an effect (must change a game state to activate Diana’s power, right?) and is thus unreliable. Can't combo with other cards well because you can only put one card under Diana per phase.
3. Olive McBride: her power is not very strong, especially at higher difficulties, and thus she does not justify competition with Beat Cop.

Attractive upgrades:

1. Reliable: for Overpower and Steadfast. Make your Machete a semi-Timeworn Brand for 5 times less XP. Your counterspells should keep the buffed Machete safe from treachery effects.
2. Shrivelling: for Prepared for the Worst. Consider Shards of the Void instead if you are playing a campaign with lots of horror, since Diana's weakness is already pretty taxing to her sanity.
3. Grotesque Statue: for Dark Prophecy. Great card that gives you a refund after its used up thanks to Diana Stanley's power. A little XP costly though.
4. Ward of Protection](/card/02307). Spread the joy to your teammates.
5. Vicious Blow

Other upgrades to consider (no particular order): Counterspell, Rite of Seeking, Shards of the Void, Beat Cop, Dynamite Blast (fun with Delay the Inevitable).