[DF] Game Mechanics for Dungeon Crawler's Guild and magic that is better underground

[finneddy]

I'm going to be running a GURPS Dungeon Fantasy campaign soon, with a specific setting that my brother and I created, and I was hoping somebody could help me out with the game mechanics.

The first question is pretty simple. I want all the characters to be an away team for the Dungeon Crawler's Guild for the region, and I'm thinking I want both a Duty (12 or less) and a Patron, but I'm not sure what the base cost should be for the Patron or how often it should show up, or even if it counts as a Patron as opposed to a job. The guild is quite powerful and rich in the region, and they offer some equipment and help, as well as training, but I'm not sure how extensive the help is.

Second question is a little more complex. Basically, in this world the farther down you go underground the more powerful magic you can do, which is why so many ancient empires have dug huge underground dungeons, catacombs, etc. but then inevitable collapsed because of some situation, whether a huge earthquake or waking up something scary in the depths.

I could just give modifiers to magic the farther you go underground, but that seems like it would really mess with game balance, what with magic users getting more and more powerful as you go farther down.

But I had another idea, which is that FP regenerates faster underground, allowing you to cast your big spells more easily. So when you're up at the higher levels you don't want to cast a big spell and wipe out all the less powerful guys because you're saving your FP, but when you get down to the lower levels you NEED those big spells, and fortunately, you can cast them with more impunity.

Problem is, I'm not sure if this makes sense or if there's a better way to do it. Does anybody have any ideas? Any help would be much appreciated.