Iron (Willed) Waitress goes to 11.

Variant of my other Agnes deck. https://arkhamdb.com/deck/view/153040

Focusing on boosting her Will such that key tasks (fighting, investigation, evasion, resolving encounter cards) are all (or as much as possible) done through Will. A base of 5 Will is good. Add in Holy Rosary for 6 and you have a good advantage on most tasks. After upgrading Peter, she can rock with a Iron Will of 7. That is usually enough for most tasks to be tackled with a good chance of success.

Key cards on your initial draw: Holy Rosary and Arcane Initiate. The Rosary because more Will = more power. Arcane initiate to help find your key spells.

Shrivelling to fight. Rite of Seeking to investigate. Blinding Light to evade.

Notes on use:

You will notice there are no skill cards. This is by design. Flat constant bonuses are almost always better than one-use.

Fine Clothes helps parley actions...as they won't be done with spells.

Lucky! can turn a fail to a win after the fact which is very handy.

Fire Axe if you need to get physical or you are out of other damage effects.

Arcane Initiate loses its doom token when agenda advances...

Storm of Spirits to clear a location of a swarm.

Need to damage a tapped or aloof foe? Take a Painkillers to heal Agnes health and get a free poke at the foe. Or let Peter soak the horror.

Peter Sylvestre is used to dump horror including from say Forbidden Knowledge and gives a free bump to Evasion. After his upgrade, he grants another boost to Will. He is also extremely useful in keeping Key of Ys in play.

Upgrades / Options

Will to Survive can get you guaranteed successes as long as your stats are high enough (and they will be).

Spirit Athame You want as many tests as possible via spells...and this knife helps you succeed on those tests. Plus it has some use as a backup weapon.

Better, stronger, faster Peter Sylvestre gives a static boost to Will and Evasion. Plus the horror capacity. Made of win.

You want both allies in play. Charisma and Calling in Favors are key to enable that combo.

If you really want a power boost with some added risk...the awesomesauce Key of Ys can rock with a +3 to all stats. With Peter in play that's a 9 Will which you use to fight, investigate, and evade. With a +2 from Spirit Athame for an effective 11 on a skill test.

Delve Too Deep is simply a method to boost XP, if you don't like the extra encounter card draw, then feel free to substitute. Starting with Calling in Favors is not a bad idea. Or if mobility is an concern, Astral Travel while not stellar, is a decent option.

Multiplayer thoughts:

With Agnes your teammates pretty much just need to buff her with Will cards when (albeit rarely) needed. In a group, she has time to build up her hand and not worry about filling all roles. That said she can pretty much head off on her own.

Again don't forget her Painkillers combo. With another investigator engaged, she can heal herself of physical damage and poke their foe at the same time without worrying about friendly fire.

A survivor player may run into issues with Agnes card selections. Agnes can start some alternates such as Alyssa Graham to keep the Will boost but Peter Sylvestre really is chock full of synergy with her horror use. If Lucky! is also taken...well...Unexpected Courage isn't great but it can fill the slot. I'd personally lean towards another spell, or even resource accelerators such as Emergency Cache or Uncage the Soul.