Mandy is not just a quintessential Seeker, she is the quintessential Seeker squared. She excels in seeking out both clues and cards, which make her one of the most powerful investigators in the game.
A of 3 gives Mandy a decent chance of resisting treacheries from the encounter deck, but with a Hawk-Eye Folding Camera or maybe two, she can easily be up to 5, allowing her to shrug off much of what the encounter deck sends at her.
Her 5 is also something to write home about. Even though Mandy' specializes in fetching cards from investigators' decks, she actually does not need any cards in play before she starts investigating. This allows her to start investigating from Turn 1, giving her a huge head start in tempo. Her ability to pull specific cards from her deck bolsters this already quick tempo, making her a powerhouse Seeker.
1 means she will not be doing anything much in the combat department--not even punching a Swarm of Rats, so you might have to rely on her 3 , which isn't too shabby. It's just enough to evade when you have to, and will make you consider cards like Trench Coat if she is going to need to evade and avoid enemies--especially in true solo.
Mandy's Ability & Card Tutoring
Card Tutoring is a term for searching your deck and retrieving specific cards. Mandy's card tutoring talent makes allies like Mr. "Rook" look delicious. However, as I mentioned earlier, Mandy doesn't actually need any cards out to start investigating...so what cards are you even looking for with her ability?!?
Don't fall into the trap of endlessly spending your actions to search for cards, which help you search for cards, which help you search for cards, etc. You're just wasting actions. You want to search for cards that can make a difference!
Mandy's investigator ability has 2 uses, which can be used by either Mandy or another investigator at her location: when she searches, she can either search deeper (3 additional cards), or more (resolve the effect 1 additional time--so draw 2 cards instead of 1). How do you know which option to choose?
That's a good question. See below.
(1) Searching Deeper (Search 3 Additional Cards).
This option simply means that if normally you would search 6 cards, you can now search 9. If normally 9, then 12. Etc. It's a great way to bore into your deck to find the cards you really need.
Choose this option when there is a specific card you want to find. Otherwise, if there's nothing you really need, use option #2 (see below).
Remember: other investigators at Mandy's location can use her ability! Most of the time, their searches (such as with Prepared for the Worst) are more important than yours!
(2) Searching More (Resolve 1 Additional Target).
This option means that instead of choosing 1 card with a search effect, such as with Eureka!, you choose 2. That's pretty good! This gives Mandy (and other investigators at her location) filtered card draw.
Choose this option if (a) hitting Shocking Discovery would be highly inconvenient, or (b) there's nothing in particular you need to search for. This becomes additional card draw with the potential to trigger Astounding Revelation and Occult Evidence.
Generally you will be searching deep at first, then switch to searching more once you have the cards you need.
A Note about Card Draw
Card draw--especially in Seekers--is a good thing, right? Right?!?
It's less good in Mandy, mainly because it means you might end up drawing Astounding Revelation or Occult Evidence (which personally happens to me all the time). Don't shy away from it, by any means, but Mandy is best served by cards that use search effects to gain cards, rather than plain ol' card draw (like with Preposterous Sketches).
Elder Sign Ability ()
You will never be sad when Mandy's Elder Sign ability crops up. At worst, it's just additional card draw--you can even use her investigator ability to search 3 cards and draw 2! At best it's a lifesaver that allows you to search up to 6 cards (when used in conjunction with her investigator ability) and commit the card you find to the test! Wow! This is really just an innate Eureka!, and another reason to ensure Mandy has plenty of good icon cards in her deck.
Mandy's signature card is singularly unique (pun intended) in that its quantity scales with her deck size. She gets 1x @ 30 cards, 2x @ 40 cards, and 3x @ 50 cards. It's not a fantastic signature card, but it's not bad either. You will know how many copies of Occult Evidence are in your deck at any given time, which allows you to plan to use her search abilities while on a location with a clue. Worst case scenario, if you draw it during upkeep, it's an extra wild icon.
Remember: just because you find a card with a search reaction (such as Occult Evidence and Astounding Revelation) does not mean you have to trigger their reaction ability--that would make it a Forced ability, instead. If you'd rather keep Occult Evidence or Astounding Revelation in your deck, rather than your hand, don't trigger their reaction ability!
As far as signature weaknesses go, this can be pretty rotten when drawn at the worst possible time. But most of the time, it's not all that bad, especially when packing Tooth of Eztlis and Hawk-Eye Folding Cameras, both of which help Mandy shrug off encounter cards. Mystic off-class Mandy has the added boons in the form of Deny Existence and Ward of Protection, which she can use to cancel the worst treacheries drawn by her signature weakness.
IMPORTANT: Cards that search your entire deck literally search your entire deck--the search DOES NOT stop once you find a card you want. This means cards that search your deck (such as Research Librarian and No Stone Unturned) WILL trigger Shocking Discovery if it is in your deck!
I wanted to take a moment to touch on Mandy's off-classes, since both her and Tony's off-class options can be the most exciting AND daunting aspects about them.
Playing Mandy in 2 player? Give Mystic off-class a nod.
This deck uses Mystic as an off-class, since it gives her the most all-round versatility, especially with Read the Signs, Ward of Protection, and Deny Existence. With a Hawk-Eye Folding Camera or two and a Tooth of Eztli out, she will be facing encounter cards with 4-6 , 5-7 , and 4 . This allows her to shrug off a lot of encounters and makes her a great target for a rogue player to pitch to using "You handle this one!". She can then use 2x copies of Deny Existence and Ward of Protection to ignore the treacheries she cannot pass. In my experience, this allows her to ignore the encounter deck and just concentrate on grabbing clues.
Playing Mandy solo? You might want to pick Rogue for her off-class. Rogue offers her a lot of enemy avoidance with action compression. Cards like Think on Your Feet and Slip Away let her put a pin in enemies while she zooms around using cards like Shortcut and Elusive (10/10 would recommend) to effortlessly suck up clues. One of your top Rogue picks should always be Quick Thinking. Mandy can commit this to an investigate test and succeed by 2 with ease, allowing her to take an additional action!
Also consider the favor cards like Decoy, Small Favor, and Intel Report. The first two allow her to buy her way past enemies, while Intel Report allows her to buy clues from an adjacent location. At worst, each of the favors has 2 icons.
Rogue offers some delectable upgrades for Mandy, such as Easy Mark, Momentum, and possibly even Pay Day.
Playing Mandy in 4-player? Consider Survivor, which has the highest clue-potential of any other off-class, if you take Fortuitous Discovery x3, Resourceful x2, Winging It x2, "Look what I found!" x2, and Lucky! x1 (though I would personally go with Lucky! x2 and "Look what I found!" x1).
Winging It gets shuffled back into her deck, and because of her card-draw, she will see it several times. Don't worry about how to discard it--Mandy often has lots of cards in hand! "Look what I found!" is a little harder to pull off, but not as hard as one might think, especially if she is working at her base 5 . It also has . Lucky! is an all-around great card that can help you with anything. As for Fortuitous Discovery and Resourceful?
Imagine this: you use Mr. "Rook", Eureka!, and maybe even No Stone Unturned to eventually find all 3 copies of Fortuitous Discovery. When you play the 3rd copy, Mandy can nab 3 clues. But if she plays it with Resourceful committed, she can also grab a different copy of Fortuitous Discovery from her discard pile. Meaning, she can play it AGAIN at maximum effectiveness. With 2 copies of Resourceful, this means she can play Fortuitous Discovery at maximum clue potential 3 times!
The other thing that prospective Mandy players puzzle over is her deck size. As a general rule, fewer cards in your deck is better, since this ensures you are more likely to see your best cards and, if you recycle your deck, enables you to see your best cards up to 4 times in a single scenario. Higher card counts dilute the effectiveness of your best cards, especially since you are limited to a maximum of 2 for most.
With Mandy's card draw, you will see and find every card in a 30-card deck likely a few times. Go with this deck size if you want to use and reuse specific cards--such as building specifically for the Pendant of the Queen. With Mandy's card draw ability, a measly 30-card deck lets her use, abuse, and reuse powerful cards with limited uses like Mr. "Rook", Fingerprint Kit, and most notably, Pendant of the Queen.
Mandy's search ability and card draw allow her to operate a 40-card deck as easily as another investigator runs a 30-card deck--and better. I personally prefer this deck size, since it gives you the option of including a few more cards than the often-limiting 30-card limit restricts you to. It also gives you the freedom to include a wider range of utility cards than usual. Going with a 40-card deck also gives Mandy 2 copies of Occult Evidence, literally doubling the number of her signature cards in her deck.
As a frame of reference, a 40-card Mandy deck will usually draw through her entire deck once in a scenario, and possibly a little more. I mention this because deck size can be an easy way to combat Beyond the Veil. I played this deck in a 4-player Return to Dunwich, and our Guardian player used First Watch to give me ALL of the Beyond the Veils that came up. With a Deny Existence in hand and a sizable deck, it made life much easier for the other investigators.
If you want to include ALL the toys and ALL the cards...go with 50. Mandy still does quite well. However, you will find that you have to include a lot of redundancies, which make that additional 10 card bump up from 50 far less effective than you'd think. You do get 3 copies of Occult Evidence, but it's not reason enough on it's own to go the full 50.
With 50 cards, Mandy may almost draw through her entire deck in a single scenario, which means it might be an option you want to consider if taking a non-mystic Mandy through Dunwich as Beyond the Veil protection.
Deck Size: How to Choose?
Choose a 30-Card deck if you want to use, re-use, and abuse a few select cards over and over again, namely Pendant of the Queen, Mr. "Rook", Fingerprint Kit, and Archaic Glyphs. You will cycle through your deck quickly, allowing you to get a second or sometimes even a third pass at your best cards.
Choose a 40-Card deck if you want a larger toolbox with greater versatility. This gives you some breathing space to include extra cards, such as a the in-game mini-quest cards (Archaic Glyphs, Strange Solution, Ancient Stone, etc), as well as more off-class cards. Mandy can handle a 40-card deck as easily as any investigator handles a 30-card deck--and then some.
Choose a 50-Card deck if you want to include everything. I personally don't recommend this, since it dilutes the likelihood of you finding your best cards, such as Mr. "Rook", but Mandy being Mandy, she can still do just fine. Just make sure to include plenty of card draw and icons.
This is an excerpt from my Mandy Standard Deck, if you'd like to check it out: arkhamdb.com