Question: how to defeat jyrik gauldurson?
Answer: tofdir will drain power from the eye, weakining jyrik. Once weakened, you can finish him off. User Info: The_Beer_Scotch. ... 
After 30 seconds, Tolfdir will weaken Jyrik, then help you kill him. Either stay back and summon a frost atronach, which can resist his frost based attacks then shoot him with flame spells.