Rulings from Alex Werner, FFG Game Rules Specialist via the official rules question form:

Question: Let’s say that Trish Scarborough is at a location with another investigator and there is an enemy engaged with that other investigator. If Trish discovers a clue at the location and uses her special ability, can she “automatically evade” the enemy engaged with the other investigator? If so, what exactly happens - is the engagement broken and the enemy exhausted?

Answer: Yes, Trish Scarborough can use her ability to “automatically evade” an enemy engaged with another investigator. Once she does so, that enemy will exhaust and break its engagement with the other investigator.

Question: Let’s say that Trish Scarborough uses Damning Testimony to discover a clue at the location of an enemy and then uses her special ability. Can she “automatically evade” the enemy even if it is not engaged with any investigator? If so, is there any effect other than exhausting the enemy?

Answer: Yes; it’s possible to automatically evade an enemy that isn’t at your location. That enemy will exhaust, even if it’s not engaged with another investigator. And while nothing additional will happen with Trish and the Damning Testimony, Trish could trigger an effect that required her to evade an enemy, like Pickpocketing. (Note, she can only trigger effects that don’t require a “successful” evade).

Ruling from Alex Werner, FFG Game Rules Specialist via the official rules question form:

Question: Let's say that Carolyn Fern has Peter Sylvestre in play and Peter has one horror on him. Then Carolyn draws Rational Thought. Will Peter heal the horror on him at end of turn?

Answer: No. Rational Thought makes it so that Carolyn Fern cannot heal Peter Sylvestre through his reaction triggered ability.

Have you ever played a Mystic deck built around recurring Premonition every turn?

Book of Living Myths is just a persistent Premonition attached to an Asset for Kōhaku Narukami decks. Assuming you keep an eye on the number of Blessing / Curse tokens and have ways to manipulate the Blurse distribution in the chaos bag, Book of Living Myths can guarantee that you draw at least 1 symbol and at least 1 Curse / Blessing token of your choice per turn. That has some unique deckbuilding opportunities:

For cards that only care about "Symbols" being revealed (assuming you use the Taboo list), like Jewel of Aureolus, Read the Signs, Hypnotic Gaze, or Ritual Candles, Book of Living Myths guarantees that you always satisfy the symbol conditions.

For cards that actively require a Blessing or Curse token to be drawn, like Eye of Chaos, Ofuda, Beloved, or Fey, then Book of Living Myths can help Kohaku reveal Blessings / Curses consistently where other Blurse Mystics would need to play Favor of the Sun / Favor of the Moon + Olive McBride to match him. Most Blessing and Curse cards are balanced around the fact that you're unlikely to consistently reveal them from the token bag when you need them; assuming you build your deck to take advantage of both Blessings AND Curses, Book of Living Myths removes that random chance altogether to the point where it almost feels like Kohaku is cheating.

This seems broken and undercooked. Insane value for what it is. I imagine this would make sense if it could be used only on enemies with trait Humanoid and the test difficulty would be dependent on that enemy's attributes.

Very underwhelming card, to be honest. Artwork is awesome, skill icons are good, and when you see a 5xp event you immediately go "wow this gotta be good". Well, it ain't! So for 2 actions, you get 4. That is basically it, this card gives 2 actions, and all without any boost or anything else. Also, you need to control a Melee asset, it can't be a gun or something else you had in mind. It is very difficult to understand the logic behind why this costs 5xp, when in the same box we got Hand-Eye Coordination which gives you 1 action for 1xp, meaning that for 2xp you get, well, this?! After all is said and done, i think i have found an explanation for this card, so hear me out:

There is a janitor over there at FFG. He works night shifts ofc, and has keys to open-up and clean each room in the building. Some years ago, and i think around the time when Innsmouth was being released, he started messing with us and started doing some "funny" things. So, when our designers distribute what will they do, they arrive at their office and what can they see? Some of the cards are already designed!!! "Sweet", they think! In their head they think the other designer has designed the card already, so even if they see the card they just read through it really fast and think "okay, he must have play-tested it so i won't complain", but little do they know that it wasn't the other designer, IT WAS THE GOD DAMN JANITOR WHO PUT IT TO COST 5xp!!!! He didn't know shit, he doesn't play this game, but he heard the others talk about XP and stuff like that, and when he was f*cking around with cards he saw those dots under the number and he thought "they won't notice that i've placed some dots there!". And those dots are, ofc as we play the game so we know, the experience cost of a card.

When all is said and done, we get cards that are so weirdly costed that it makes no sense, like Flute of the Outer Gods, Signum Crucis (which they realised after 2 years and changed it to 0xp), Blood Will Have Blood, Quickdraw Holster, Rod of Animalism, Clean Sneak, Katja Eastbank etc. In this campaign he got into the room couple of times, as we can see in the cards like this one Flurry of Blows, Stir the Pot, Providential, and ofc let's not forget that one time he said "fck it" and deleted all the new text that was supposed to be on the Fire Axe and just typed in "Fast" as a funny joke describing how fast he comes in and changes things without anyone noticing.

I think after all is said and done, FFG has really gotta do something about that guy, as before that guy started messing with us we would get maybe some cards that are completely out of the way, but in the last couple of expansions there is some weird shit happening around XP costs and effects, but not in all cards, just some so they don't figure that guy out, but i have figured it out!!!

Janitor, if you're reading this, know this = we will get you and feed you to a Shoggoth, you son of a....