Each person, no matter who or what they are, take to magic completely different from another. Some excel in light magic, others in shadow. One simply needs to learn how to master it first. But, depending on what you are you can only use your magic for so long before it corrupts you, hurts you, or kills you.
Brotherhood of Light:All Brotherhood of Light Knights know how to use Light and Shadow magic. But they can only use it for a limited amount of time before they become drained and exhausted. Some knights excel better in Shadow magic, which helps deal more deadly attacks when fighting the armies of the Dark Lord. Others excel in Light Magic which is use to heal and purify. It all depends on the knight who harnesses the power.
Witches and Wizards:Witches and Wizards draw their magic from different sources, some use nature other use human sacrifices. Those who use sacrifices become tainted much faster than others. Though they are powerful witches and wizards are human and still live by the laws of mortality. They can extend their life but can not live forever. They age normally, no matter if they extend their life time. Magic easily corrupts humans and turns them into evil creatures. They are limited by how much magic they use, their mortal bodies can not withstand the strain of overpowered spells without help. Witches and wizards can also absorb the powers of others by killing them and drinking in the essence.
Necromancers:Necromancers are extremely powerful sorcerers who draw their magic from the dead and the Lord of Death himself. They have few limits to their power. Complete concentration is needed when controlling their dead underlings, if they are not careful their minions will turn on them. Too much magic will tire them out leaving them open for attacks from their enemies so use your magic wisely.
Vampires:Few vampire's actually have magic, Carmilla, the Vampire Queen can summon electricity in her hands and use it against her enemies but only older powerful vampires can use magic. It is not to say that younger vampire don't have magic it is simply that they have yet to unlock it. Most Vampire magic is based on an element such as, water, fire, earth, air, metal and electricity. However some have had the ability of moving things with their mind and reading others thoughts.
Lycans:Lycan's can not use magic
Fae:Fae come in all shapes, sizes, and races. There are fairies who use magic to help others, heal wounds, and play tricks on others, elves with enhanced speed and eye sight, and trolls with the power to break boulders in half with their bare hands. The list goes on and on, each Fae have their own special abilities and each with their own limits. If you choose fae be sure that you keep them balanced with power and weaknesses.