First of all, the following contents include those which might spoil your game, because of their power, usefulness or fatality to your game in wrong use. All I ask is that you agree to protect yourself, and agree not to complain even if your game should be broken. If you are not confident that you can use those without spoiling your game, I would strongly recommend you to ignore the following contents.
Miscellaneous
Prying Eyes
Is sold by Mystina in Julienne's shop. It shows the attributes and skill levels of a target.
Summon Unicorn
A staff named "Unicorn's Horn" is sold by Mystina. While the staff lies in your inventory, you can use the spell of "Summon Unicorn". You can summon a unicorn anytime and anywhere.
Mystina's Great Magic
You need three things in order to use the spells "Celestial Judgement/Storm", "Meteor/Meteor Shower" and "Tornado".
1 : The book "Mystina's Great Magic" (in Mystina's invetory)
2 : The staff "Unexhausted Sorcery" (in Mystina's inventory)
3 : Your skill level of Destruction being Master
To learn the spells, you will have to get the book that teaches the spells in the first place. After Mystina joins you, you can take it from her inventory. The book being added to your inventory, you will learn the spells. To use the spells, you need to equip the staff "Unexhausted Sorcery" as well, which also lies in her inventory. Nothing will occur if you cast the spells without equipping it. In short, you can use the spells only while you equip the staff. Although the staff brings you a huge quantity of Magicka and allows you to use the Great Magic, but it costs you Health and Fatigue everywhen. Care must be taken.
You will find Mystina sells the scrolls of the same spells. If you will use the scrolls, you do not need to take any trouble to use the spells except for unbelievably much money.
Celestial Judgement / Celestial Storm
Calls thunderbolt from the sky onto a target/targets. No one will survive the thunderbolt. Its effect does not spread widely. While there is little risk of its damaging you, it would be a little difficult for the thunderbolt to strike a target moving around. It would be wise to use the spells towards those who attack you without moving, like a mage or a marksman. The spells can be used only outdoors.
Meteor / Meteor Shower
Calls meteorites from the sky onto a target/targets. Its explosion spreads widely. While it would be easy to damage a targets/targets, there is much risk of damaging yourself. The spells can be used only outdoors.
Tornado
Blows away targets to the sky, and then they will damage when they crash onto earth. The spell can be used only outdoors.
Incidentally, the staff "Unexhausted Sorcery" may be not bad to use in combat. The target would be attacked by eight spells from all around. The name of the magic is 'Prismatic Missiles'.
Prismatic Missiles
Evil Magic
To learn the spells, you will have to find an extra comapanion and have her join you in the first place. She has a book that teaches you the spells. You can take it from her necromatic stuff box. The book being added to your inventory, you will learn the spells.
Summon Evil Rat
Summons a rat that fights for you and attempts suicide bombing as soon as attacked. You can summon as many rats as you like. Regarding further information, please read the book in the game.
Summon Hell Hound
Summons a hound that fights for you. Its burning skin damages those who attack the hound. You can summon as many hounds as you like. Regarding further information, please read the book in the game.
Vanish
Vanishes any NPC/creatures. Never will he/she come back. Again, NEVER. This spell is provided just for fun. It can vanish even an essential NPC. Also, it can vanish some other things as well. It can break your game easily. I strongly recommend you to use it only when you are enjoying the game in save data that is not important. Again, this spell can literally break your game easily if you should use it carelessly.
For information of people who know the script of Oblivion, another description is as follows. In short, this spell allows you to simply 'disable' a target. You know its risk of breaking your game.
Ring Of Necromacy
While you equip the ring, six undead creatures follow you and fight for you. The price you pay for this is your Health, Magicka and Fatigue. The three of yours will be being absorbed while you equip the ring.