First, SuperPower Wiki documents the most powerful forms of each ability, so it's only a guideline if you're using it to figure out the rough principles of something. For the record, Omnipotence is only a valid relation to Entropy Manipulation if you don't actually know what Entropy is and just think it's a cool word.
There are two kinds of entropy, the one I'm addressing is Thermodynamic Entropy. Basically, whenever you have anything happening, you have entropy. Not all energy is useful - in every reaction, a small amount of energy is lost as useless heat energy. Eventually, the universe will run out of useful energy and completely dissipate into the most simple forms possible - a random matrix of Quarks. Entropy is also the order of something. The more ordered the molecules, the lower the entropy. Thus, a gas, with atoms moving randomly and completely unbound is in a higher state of entropy than a solid, whose atoms are aligned in a lattice fashion.
So in short, the important part is: Energy In = Energy Out + Entropy. My character is going to ignore molecular entropy and focus only on reaction entropy (so she won't be able to turn rock into gas as a full Entropy manipulator could). By increasing the Entropy of a system, the Energy Out must be decreased thanks to the above equation (making the reaction less efficient - a fireball spell might only convert 95% of the used energy into the fireball, instead of 98%. By decreasing entropy, the system can be made more efficient. By removing entropy completely, you get 100% efficiency. You could force friction to slow bullets down more quicky, for example. By reversing entropy, you can overcome limits and create over-efficiency - that friction from earlier you can make become over-efficient and slow down the bullet even more than it physically should be able.
