One thing going through my mind right now are top-end druid spells for a megadungeon campaign.
Right now, PI 5 and PI 6 for Druids are pretty sparse:
PI 5: Alter Terrain, Arboreal Immurement, Create Elemental, Entombment, Partial Shapeshifting, Permanent Beast Possession, Permanent Shapeshifting, Plant Form Other, and Shapeshift Others.
PI 6: Earthquake, Geyser, Move Terrain, and Volcano.
We've got a druid with PI 5 and enough points for PI 6 and one spell.
And I'm not sure I like where that is going for a megadungeon campaign. I have some very strong reservations about the PCs using Earthquake, Volcano, and Alter Terrain willy-nilly in the dungeon. It'll be hard thanks to layered penalties of worked and altered stone with magic resistances built in vs. a druid penalized for being underground, but even so - do I want to build a giant multi-level dungeon so the PCs can blow it up whenever they hit an obstacle they aren't sure about?
Do I actually want volcanoes and to have to figure out what happens when levels 2-4 collapse down on and pancake the secret sub-level I designed with such care and wipe out the entrances to levels 5 and 6 because, hey, it says here that "Severe" level casting means we can drop the roof on those orcs? They just might be inappropriate for this kind of game, but something good needs to come with top-end Druidic PI.
Not that PI 5 and 6 aren't in and of themselves useful, but they should at least have a few useful spells.
I'm debating chopping the list down a lot.
Create Elemental is pretty much a "grind the session to a complete and utter halt" spell cast in play; cast outside of play it's useless, so I will cut that off.
Alter Terrain and Move Terrain don't fit. I might allow them, but just flat out say "outdoors only." If/when we go on wilderness hikes, if the PCs really want to do this, maybe it's okay. In the dungeon, yeah, I put in a lot of work mapping, stocking, prepping, etc. for 1 character point on a single PC and a good die roll to undo it.
Volcano would be gone. I see no way that provides any value to a megadungeon game, and I can see a huge list of downsides.
Earthquake can probably stay, but again, I'll need to firmly enforce a) restrictions and b) consequences. By restrictions, I mean, if any of the area affected has a penalty for druids and/or magic resistance, it affects the whole area (even one bit of worked stone in an area is -3 or higher for the druid, and if it's -10 Magic Resistant stone, well, -13 to cast), make it clear you can't get cute and throw it vertically instead of horizontally, etc. By consequences, I mean, when the dungeon collapses it's going to spill into multiple areas, including where you might be. And it might not even fall. So it'll be largely useless - castles and dungeons won't exist purely on the sufferance of angry druids.
I might expand the list. Spark Storm makes sense. I could make another outdoors version of the Rain of spells to allow druids to call down lightning strikes in an area. Rain of Lightning would be a trivially easy spell to stat up (outdoors only, again.) Maybe a lasting version of Control Elemental. They should have access to at least a few spells of special note . . . but they shouldn't be megadungeon destroyers just because, well, DF1 says they have those spells.
And it's worth noting, wizards and clerics can/t/don't/won't have these either.