[quote=@rextremendum]
Conservation of energy is the main thing: is energy in >= useful energy out?

Also, on the topic of life and death powers, how do they work and what are their capabilities? From what I understand about life it is the manipulation of organic materials, but how does a person use it without knowing what the fuck is going on on a molecular level?

Also, I completely forgot to ask, but what is the approximate technology level of the setting? Is it roughly analogous to a year range of earth history, or is shit all over the place?
[/quote]

Basically conservation of energy, but with the chemical energy in your body added in and converted to that form at various levels of efficiency.

Life is essentially bio-energy.  If you add it to a cell, that cell either has energy to burn or, if you give it enough, it splits, leading to healing powers.  Death is the opposite.  It lowers the chemical energy in a cell, weakening its function or killing it.

As for tech, some of the world is Late Medieval, some is early Renascence, depending on the wealth and overall society of an area.  Warlike societies, for example, aren't going to have any use for bicycles, and little patience for dirigibles.