Magic: people must be born with a innate ability for magic but they can acquire artifacts that boost their ability  using magic drains a person of energy but the greater the apptitude for it the greater reserve they have some of the dark mages drain life out of living things as energy there are tour types of magic
Elemental- uses fire earth air and water for their bidding a low magic user or a beginning mage can only do 4 spells or incantations they must also choose one of the four elements to specialize in.
Necromancy- the power to raise the dead and commune with spirits mages just starting out with this type of magic can only resurrect animals at first 
Healing- this magic heals wounds but also as mages become more skilled they can infect enemies with a rot that kills them from the inside out 
Telepathy- telepaths can read the thoughts of others and use their mind to control men weaker than them and also move things with it a skilled telepath could bring the most noble man down to a shrinking coward if mages start of in this school they can hear thoughts 
Rules to using magic- 
New mages do not get a whole bunch of spells  they must choose what category it is that they specify in it you would like to create a new category run it by me and it it's not to op then I will say yes a mage can't cast spells forever you must show your character getting weaker or show when a huge spell takes a tool on them