My fantasy world Treyidal tentatively has a pressure based magic system. This started as an outgrowth of the inability of my merfolk to do a whole lot, and this is my hopeful solution to construction, forging tools, and combat.
However, I've found it difficult to work on this. For one, I've found it hard to find the information I need on how this would work, and how I could deepen it (like with different forms). I know that on the most basic scale, a stone block is carved of sorts and is used to place pressure on a magical implement called a pestle.
Overtime the energy from the pressure is stored into the pestle, and then by applying pressure later on, such a pestle can be used to heal wounds, other types can be used to harden sand into a stable building material, and so forth.
The problem is is that while I find this interesting, it feels a bit too restrictive for my purposes. Namely, I want the magic to have a combat use, and the magic needs to be able to transform a character into a merperson (obviously with this one they can stamp the pestle all over the human character, but considering I need two characters to be transformed as they are drowning, this isn't nearly fast enough.)
Further explorations in this will involve how this magic is used by humans, and may involve plate tectonics, but I'm not sure how that will work.