Another trauma signature weakness. Looking at the two elements, the effect and the discard condition, we get:

The effect: It drains Akachi's charges by forcing her to exhaust spells to build up 4 charges on this card before the end of the scenario, or face a physical trauma. Since Akachi usually has plans for those charges, this is a bad situation. While her Health is better than Roland's Sanity, physical trauma is still no joke and can end the scenario, especially since, like the whole suite of trauma weaknesses, if Akachi is defeated before getting the requisite charges on this card, she gets bonus trauma! On the upside, other investigators in her location can move charges as well, although it's not that common to have other spells with charges floating around. The largest problem with mitigation is that you want cheap spells with #+ charges, and they pretty much all take up Arcane slots that you already have plans for. You could use Sign Magick or Familiar Spirit to get more Arcane slots, but that is increasing the cost overall. Useful, low-cost spells include Alchemical Transmutation, Clarity of Mind, Healing Words, Mists of R'lyeh, and Song of the Dead, and Akachi's ability makes sure they have plenty of charges. One significant advantage to this card over other trauma weaknesses is that you will generally have two spells out, and Akachi can exhaust both of them in any free triggered ability window, allowing her to fill this weakness in two turns, drastically reducing the danger of a very late game draw. Now that Brand of Cthugha (4) exists, it would be pretty easy to siphon some of those 9 charges toward this, assuming you weren't the primary killer on your team.

The discard condition: None, but, if you get 4 charges on this card, you disable it (and it does not get discarded).

All in all, this is an average signature weakness.

This is a very tailored signature weakness, and it's a thing of beauty. Looking at the two elements, the effect and the discard condition, we get:

The effect: This is a very unusual signature weakness, and it's a little hard to get your head around. Minh likes committing cards. It's pretty much her whole deal, and this card messes that up seriously. She gets to either not commit anything, or commit 3+ cards, which taxes even Minh's prodigious draw. If your luck is bad, you can end up spinning your wheels for a couple of turns, trying to amass enough icons to clear this. Fortunately, as farmstrong points out elsewhere on this page, the card draw that helps Minh draw this weakness also helps her get the cards to clear it. Sadly, as one of the investigators most likely to deck herself, Minh is at somewhat greater than normal risk to draw her signature weakness more than once in a scenario.

The discard condition: One of the most difficult (well, at the very least, finicky) in the game so far. Minh has to commit 6 matching skill icons to a successful test while committing at least 3 cards. First, you need to succeed, so and tests are best. If you are lucky (and prepared), you draw this in upkeep and clear it with a treachery in the Mythos Phase, otherwise, try and Investigate a low-shroud location. Obviously, cards with multiple icons are great, and cards with multiple icons are even better. Minh's ability and Grisly Totem can help boost the total icons, but, since you need 3 cards, they are more insurance than necessity. Other obvious cards are Inquiring Mind, Unexpected Courage, Guts, Perception (2), and, really, anything with at least 2 , , or icons. There are about 30 in alone. The good news is that you will usually be testing 10 vs 3-4, so the chance of clearing this on the first try are good at any difficulty. The bad news is that the exists.

All in all, this is an average signature weakness, a serious speed bump but unlikely to end a scenario.

The easiest way to handle this weakness is that you draw this card at the round when the agenda will be advenced like Arcane Initiate. Lucky Cigarette Case (3 level) is the good way to find this weakness. Also, some cards help you to find this card; sadly, he cannot take Rook for that.

Otherwise, you commonly want to defeat this enemy because of 1 doom. Here are some good cards to handle this. Note that he may want to deal 1 damage because most weapon has 2 damage (Long Colt, Switchblade, Mauser C96, .45 Thompson, Knuckleduster...).

• Marksmanship: This saves 3 actions; 1 engage, 1 move, and 1 fight. He could use his extra action to fight with Marksmanship.
• Righteous Hunt: This saves 2 move actions, and gives 2. He could also use his extra action to play this card, because this card has engage.
• "Get over here!": This save 2 actions; 1 move, and 1 fight, and potentially 1 action. This make the enemy move, so he may save 1 additional action if he need to his original location. One sad thing is he cannot take 2 level version.
• 1 more damage: Vicious Blow, Delilah O'Rourke, Garrote Wire...
• extra movement: Nimble (even if his is low, and hard to find test), Shortcut, Elusive...

Unlike all the other "If you fail, you must either ... or ..." effects, this one does not contain the word "must", which implies that you can choose to place 2 clues on your location even if you have none.

The section "Must" in the rules reference says: "In the absence of the word “must” while choosing among multiple options, any option may be chosen upon the resolution of the effect—even an option that does not change the game state."

Or am I missing something? Could this be an oversight by the designers?

I think an overlooked use case for this card is in Daisy Walker. Her willpower isn't that great, and it isn't often worth using spells that don't boost , and the ones that do boost it are too high level for her. She's not too likely to use arcane slots aside from Arcane Enlightenment or some other niche cards.

Obviously she's never going to substitute , and she doesn't need to. And it seems at first that getting a boost of only 1 to (without extra damage) or isn't really worth 2 xp, 1-3 cards and both arcane slots, but the most important consideration is Higher Education. Since it's a permanent, this combination of cards can convert any test to something that can be astronomically boosted with only a little bit of money, something that's easy enough to come by as seeker, and cards in hand, which are also easy enough to come by in that class.

It's not something that lets you fight primarily, but it can finish off a weakened enemy, and it can let you evade when desperate. It's also good at dealing with the rarer or even treacheries.

Also worth a consideration are all the seeker cards that interact with secrets. Eldritch Sophist and Truth from Fiction let you keep it around even longer, and the former lets you move charges from it to stuff that's more useful as the situation calls for. With that in mind, the three copies can be extra easy and fast secret gain, for use with other great secret assets, of which a few have been teased for the Innsmouth cycle. Though some of them also compete for arcane slots, Daisy can run Familiar Spirit in a pinch, or just run the very best slotless or Tome assets that use secrets. Old Book of Lore is a particular standout.

Overall, it isn't really necessary, or something that seekers don't have tools for already. However, most of these tools are events, and having something permanent - secret supply notwithstanding - on standby for turns where Mind Over Matter would feel like a waste is pretty good.