Must haves

• Ally : https://fr.arkhamdb.com/decklist/view/4321/agnes-deckbuilding-guide-expert-3.0 Says Peter Sylvestre advanced is better than Arcane Initiate, but you absolutely need your spells fast, so Initiate until you find 1 or 2, then peter (also getting rid of the doom, and so you don’t realy need to upgrade her)
• Spells : mulligan hard to have them
  • Wither : no charges !
  • Storm of Spirits : remember extra damage goes to principal target ; so 1life ennemies « generate » 1 extra damage to the primary target
  • Mists of R'lyeh : some monsters are too big ; do not overlook this card
• Investigation : Agnes is geared towards dealing damage, I think you should dedicate to it (hence Mists of R'lyeh)
• Fighting with : just…why ? Get Wither
• Someone must heal her horror and have the Hallowed Mirror (upgradable)

Options

(take 4, not counting Esoteric Research)

• Esoteric Research : Agnes takes a lot of horror ; do we want 2 traumas more ? Also, The Rabbit Hole already gives +2xp / scenario. It depends on the healing capacity of your team. Delve Too Deep seems more flexible : maybe one of each ?
• Forbidden Knowledge : In this build, Agnes does not seem to struggle for ressources, so this is essentially a horror taking engine ; maybe not with Esoteric Research ; maybe if your pair with a healer, like https://arkhamdb.com/decklist/view/12218/a-witch-and-her-shrink-carolyn-deck-super-fun-1.0. Also, one more asset which means a clunkier deck
• Arcane Initiate : you NEED your spells, and mulligans+draws is not always enough. But this is one more assets, so it gets clunky, and one Doom is a heavy price in multi-players games ; anyway, do not upgrade her, but sacrifice her (by playing Peter for example) before the agenda advances
• Delve Too Deep : replace by Time Warp at mid-campaign ; xp is less valuable after that
• Drawn to the Flame
• Ward of Protection
• Deny Existence
• Guts : replace by Four of Cups when possible (Spells and Peter are priority)
• Premonition : rather than Guts if you plan on keeping the card