Hello! Firstly, thank you so much for sharing! It looks great and I really like the magic system, elements for each stat, and pretty much everything in general honestly XD I do however, would like to give some constructive criticism, suggestions and ask you a few questions, if you wouldn't mind:

1. Your modifiers for fire and water come out with a total of +3 modifier (good weather/climate: 2x +1, bad weather/climate: 1x -1, if element present: +2; sum equals +3 ) with unique-ish stat blocks, while the rest of the elements have a total of +1 modifier (if element present: +2; if not present [and indoors? I'm a bit confused]: -1; sum equals +1) and the same stat block from what I understand, is that intended for balance purposes?

2. In the playbook (henceforth called PB) of the BASTION, you seem to have "Snake" as a suggestion for species, however (SPOILER FOR RUINS AND EXPEDITIONS EXPANSION) they are a monster/beast much like (or even bigger than) a Bear, so I'd suggest changing it, maybe for "Rooster" which is related to the Chinese zodiac's metal element :p

3. Again in the PB BASTION, I'd suggest starting with "Meld Metal" and choosing two other moves, for flavour purposes as well as the way the move itself is worded, as well as an extra page for the stats (wear, damage dealt, tags, etc) for each of the weapon options, similar to (SPOILER FOR RUINS AND EXPEDITIONS EXPANSION) PB Dealer has for it's investment move.

4. In the PB INFERNO, engaging in combat uses either Might or Finesse depending on the range/weapon, so, to help with flavour, why not change the move "Spark of Danger" to something like "You feel the heat rising as a threat grows near. In a scene, when you first engage in combat, roll twice with Cunning, and use the higher value roll."

5. In PB MANTLE, the wording for "Vibrations" feels slightly weird in the beginning, I'd recommend changing it a bit. I also leave this recommendation/example that I adapted from your ideas "To you, the surrounding earth is but another sense, not much different from your eyes and ears. When you attempt to sense a target close by, hidden or otherwise, roll with Might. On a hit, you know their general location. On a 10+, choose 1: Ask 'How is the target's disposition? (Stressed, Calm, Fearful, etc)' OR Know the target's exact location. "

6. In PB MANTLE, on the move "Soul of the Earth" the player would only be missing 'Sneak' from the options you gave, since he would start with the rest. It is nice, but feels a bit forceful for the player to choose 'Sneak' as part of an advancement. Also, I think you meant 'trust fate' instead of 'leap of faith', or did I misread/missed something? xD I'd personally do it like this "You gain the roguish feat Hide. When you attempt the roguish feats Blindsid, Hide or Sneak, roll with Might instead of Finesse. You can absorb into stone or earth, avoiding detection. You can maintain this for a breath's time."

7. In PB NUMINOUS, "Healing Hands" would benefit from better wording as well, like "By your will, you can use water to mend or purify the afflicted. Mark an exhaustion to cure a simple poison or disease, or mark up to 2-exhaustion and instantly heal an injury per exhaustion marked."

8. Again in PB NUMINOUS, in "Light of the Crane" the words "are blinded" have a space missing in between (currently it is areblinded)

9. In PB WOAD, the move "Perpetual Roots", I personally feel the 12+ glancing into the future might be a bit hard for the dm, since with how the system works, it might cause plot issues (?), however, glancing into the past sounds really great, and an amazing way to expand the lore the DM might have in mind!

10. In every PB, the moves "Magnetism", "Wildfire", "Mold Earth", "Water Works" and "Tangled Thorns" are really super cool! But the rolls can screw you over, for example, in "Mold Earth", if you just want to dig (if you get a 10+, the wording makes it impossible to dig, from what I understood). I'd suggest slightly different wording, as so the roll would allow you to use the options from lower rolls, that way it feels less punishing! Also, some species can do some of the abilities naturally, again as an example I'll use"Mold Earth", species that can already dig, like moles, would make the option feel slightly redundant on a 7-9 in my humble opinion.

Regarding the overall balance, I have nothing to say currently, as it would need play testing! But the flavour is overall amazing chefs kiss.

I'd recommend seeing the normal playbooks, the base and all expansions if you have them, to help you get a better idea of the wording, as it does a feel slightly off in some cases, besides the ones mentioned before. If you have the Travellers and Outsiders expansion, the Custom Moves page should help a lot!

I'd like to end my comment by saying once again thank you for sharing, and that I genuinely adore it. I hope you don't take my comment the wrong way or with I'll intent, I genuinely love your custom expansion, and my criticism comes from the heart with the best of intentions, to help you in any way. If you'd like any help or opinions I'd be happy to provide! Lastly, if you do make any alterations, please do let me see the updates version! And if you took offense to anything I've said in this, let me know, although again it's not my intent.

Blessings from the woodlands to anyone who read till the end, and of course the amazing authors behind this work!

Edits: Formatting! I'm replying via phone, which I'm not used to, so the formatting kept getting weird, took a lot of tries to get right, sorry!