If you have a talent, like 'true sight', or 'unstoppability', give the reasons for having the talent or ability, and again, describe it as thoroughly as you possibly can as if it were a power.

Also, give information on the power levels of the spell as compared to other magii. Now this is a tricky thing—how do you rank mages. Mages are ranked in terms of three things: the innate magical ability of the individual, the experience at the task that the individual has, and the circumstances of the moment. Nice and specific, eh?

In addition to describing each and every spell or talent that the mage has, it's entirely reasonable to have a note describing overall powers and limitations of the mage—things such as planar restrictions, spell frequencies, recuperation from use, et cetera.

The best advice that we can give regarding writing up a mage character is to simply provide as much information as possible on each and every spell given and to be reasonable about the ratio between the number of distinct magical abilities, the proficiency with those abilities, and the power levels of those abilities. Keep in mind how very ancient Selene is, the highly out of the ordinary training received by Doctor Strange, the lineage of Margali Szardos and Amanda Sefton.

Kitchen witches are common, we all have some manner of magic in our lives whether it is acknowledged. People capable of outwardly shaping the reality shared by more than one person are rarer. Magical artifacts are rarer still.

Just keep in mind that even though we are in an offspring of the Marvel Universe, Alexandria was still burned, witches and gypsies and midwives were still persecuted and slaughtered, and there are beings like Eternity and the Living Tribunal and Doctor Strange who all to some degree police interdimensional activity. Feel free, when in doubt, to discuss your concept with any of the Wizards on the MUX.