That still is a violation of entropy because you’ve increased the “order” of energy in the universe as a whole, which is not possible.
If you can violate entropy, one can create a more than perfect Carnot Engine (or in general just a heat engine with efficiency greater than 1) which would allow you to generate an infinite amount of energy in the form of mechanical motion.
Unless in creating/gaining “mana” one is accelerating the entropic decay of the universe as a whole equal to or greater than the amount of entropy reversed locally (eg spells must produce heat and be inefficient at converting mana energy into work), magic would violate thermodynamics and allow for infinite energy creation.
I have had the same thought before. Unfortunately conservation of energy is not enough to ensure entropy is monotonically increasing.
Say you created a tiny universe with the same average entropy of our universe and then you connected it to the edge of our universe. Energy is not conserved because you just added some, but entropy is because you didn’t create an entropy potential.
Say you had a warmer object and a colder object and you took all the heat energy from the cold object and added it to the warm object. The energy of your system was conserved, but its entropy decreased, violating the second law.
You can use violations of the second law to violate the other laws because entropy naturally wants to increase due to probability (which cannot be violated without destroying math and logic etc.).
In the scenario above, if you put some fluid between the two objects you could harness convection via a turbine to harvest energy. Even though your action of moving energy around didn’t create or destroy energy, it created a sort of entropic potential energy. Kind of like how teleporting an object to a higher elevation doesn’t really increase any energy in the universe since all mass and kinetic energy were conserved, but you’ve now increased the potential energy of the object which would become kinetic energy as the object falls back down. You could then harvest infinite energy if you repeated the cycle.
In order for one to move energy around via magic without violating entropy, one has to increase the entropy of the universe by at least the same amount it would take to move that energy without magic.
The solution I thought of was just that magic accelerates the expansion of the universe. Technically this still allows for some “impossible” stuff locally, like a perpetual motion machine or free energy generator that will eventually die but on the timescale of human lives seem infinite.
Magic would get weaker with use over time as the universe nears it’s equilibrium temperature, and you would be shortening the lifespan of the universe every time magic is used. But even if you used it excessively, you probably wouldn’t be shortening the lifespan of the universe by very much unless you were using magic to like move black holes around or rearrange galactic clusters.