Alteration Ritual Spell

You have mastered Alteration spells, what is next?
== Walkthrough ==
Once you have reached 90 skill points in Alteration, a new conversation option is revealed when speaking with Tolfdir. If you ask him 
:"What else is there to be learned about Alteration magic?", 
he will mention that he has been working on a new spell, but requires Dragon Heartscales obtained with a special dagger known as Kahvozein's Fang. 
He will then tell you where you can retrieve the dagger. This location could be any of the following:
* Forelhost
* High Gate Ruins
* Lost Valkygg
* Ragnvald
* Valthume
* Volskygge
Proceed to whichever dungeon Tolfdir mentions and retrieve it.
Note: This dagger can be found by simply exploring Skyrim, so do not be surprised if no dagger location is mentioned by Tolfdir.
=== Use Kavohzein's Fang to collect Heartscales ===
Next, find a dragon. It does not usually take very long for one to appear. Once it has been defeated, use the dagger to retrieve the heartscales.
=== Bring Dragon Heartscales to Tolfdir ===
Return to Toldir who will reward you with Spell Tome: Dragonhide. Thereafter, he will also sell Spell Tome: Mass Paralysis.
de:Der Veränderungsritualzauber