The Monster Manual is a really clean design and a fun way of cheating on mana, even if it's likely not viable in most of our cubes. Notably, the adventure is *almost* playable on its own, but paying 6 mana to cheat a creature is way too much, even spread out over multiple turns. In a deck with lots of cheating targets or creatures with burdensome additional costs or ways to draw a lot of cards this looks sick, but that's a lot to ask.
I will admit I'm a sucker for UW planeswalkers that do weird things. As such, I'm pre-tempering my expectations with Elminster. However, like with Nalia in Miles' post, I love top-of-library manipulation, and this card fits the bill. I suspect it's a fine finisher as a swarm of 1/1 fliers is hard to deal with, but decks with this card might want to load up on cantrips, which could easily be a nonbo. Great with X spells.
Speaking of Nalia, Faldorn looks surprisingly good if you're loading up on impulse draw, and it goes great with Into the Wilds, one of my favorite RG cards from recent years. The second ability looks kind of funky written as it is, though I understand why it needs to be that way.
The other two are cool but don't spark joy for me.
I'm not usually into this sort of thing, but getting a Hill Giant version of this effect is nice. Overall, I'm with Miles in that the set looks mediocre so far, which is great.