These cards are absolutely 100% crazy nutso bonkers good. I thought they would be ‘ok’ after all they’re quite expensive and limited to a once-per-turn boon but I was deeply wrong in that analysis. Play Sefina and investigate once per turn as if you were a 4 intellect Seeker. Punch an enemy or a locked door at 4 despite being a weak butt. Evade that 20 health monstrosity despite being some slow loser like Jim.

They’re slow and expensive, an issue which is only slightly salved by Uncage the Soul and finding the ones you want can be difficult unless you invest in Lucid Dreaming so I could see this being an issue on ‘sprint’ scenarios like Essex but they’re still far too good to pass up. In my opinion they slot best into Sefina right now as they complement her dawdling, defensive stat line nicely, she can make better use of the Alacrity boon than most, and she can more readily pay for them.

I don't see much use of any of the Empower Self cards.
Most Mystics will prefer to use their willpower since it's likely to be their highest stat, plus it takes up a highly coveted Arcane slot.
I can see it appearing in a Werewolf Diana Stanley deck, particularly in the Eldritch Knight variant.
Outside of Mystics I doubt Patrice Hathaway can truly capitalize with her low ,, and , particularly on higher difficulties.
Sefina Rousseau is plagued by the same limitations, while also having it compete with Double, Double (4), Borrowed Time (3), and Suggestion (4) for the Arcane slot.
Intriguingly, I can see a support Daisy Walker taking this, with limited competition for her Arcane slots and ability to maximize its utility combining with Encyclopedia (2), Strange Solution (4)
Norman Withers might be able to make use of Empower Self: Acuity, but the not much of the others. Besides, I'd prefer to use Scrying (3) as well as Shrivelling (5)/Mists of R'lyeh (4) on the Arcane slot over Empower Selves.

Did I miss out on any investigator who is able to pick up Empower Selves?
Or any combinations that maximizes its utility?

This looks fantastic for Minh Thi Phan with Analytical Mind.

Not only is Minh more likely to interpret the dreams successfully over the course of a scenario (with the need to over-commit for The King in Yellow), Minh can effectively give a +2-5 (possibly +6/7 with Grisly Totem (3)) boost to any skill test for any investigator each round, with greater flexibility over turn order as well as the option to save it for the next round.
With Dream-Enhancing Serum, Minh should easily be able to reach and hold 8+ cards in her hand each round.
Unfortunately, it will take up one of her hand slots which is generally reserved for Ancient Stone (4) and The King in Yellow, albeit the latter being involuntary.
I can also see this doing well in a Daisy Walker deck.

Any other suggestions on who else it would be good with?

This is really good in Jim, particularly in TFA and Carcosa due to the nature of their Chaos bags. Both bags have a tendency to just be Skulls + 1 other symbol based on your route.

Let's look at Echoes of the Past on Hard. For Jim, assuming he has Recall the Future in play and names the Cultist/Tablet/Elder Thing (whichever there is two of in the bag, which is how the bag will be unless you Doomed out at the party), the bag is:

7/17: 0 or greater 2/17: -1 4/17: -2 2/17: -3 1/17: -4 1/17: -5 And as always, 1/17: auto fail

Assuming for another investigator that the Skull is passed when at -2 you're looking at a change from 64.7% success to ~76.5%. That is quite the gain, and Jim pulls significantly further ahead once the Skulls breach -3, which isn't unheard of in this scenario after the mythos phase.

The thing is this card effectively gives you that same ~12% boost to your success rate until you actually need it. It's just like Lucky! in that sense.

Lucky! is more powerful per use of course, but you don't get it back every single turn. Playing more aggressively against the odds and knowing you have a way to get there anyways allows you to conserve your resources and gain tempo.

Just be careful to name a token that will actually make you pass a given test. Recall is not optional. If you call your shot, you get your +2 so make it something that actually counts. Especially vs Mythos tests you might not care about, try to name something you only have a 1/17 or so pulling.

Still, I encourage you all to try this in your Mystics and off-class Mystics. Lucky! is a genuine consideration in any deck that can take it, so don't sleep on Recall if your deck building restrictions don't allow taking it.

2 resources and 1 card for 1 action, but 2 cards and 1 card worth 3 actions, so 3 actions for 1 action? Not an impressive card among all those rogue cards providing action. But when export to other factions with Versatile, this ability become priceless. Seekers draw cards so easily, that you can almost consider cards as free. So 2 resources for 1 actions now? If there is any card can get resources as efficient as 1 action (you don't have to count in any cards spent!) for 3 resources, then the combination will become 1 free resource! And then you just use the free resource for more actions! Here is a deck for example.