Thornfire wolf have 600 hp and it's weak to ice (105% damage). So to me the best strategy is to hit with a weak weapon until they are on red life and then you stop attacking. So, you bring him to water and as soon as he walks in water, you hit with your powerful weapon, making sure this hit takes what's left of his life. You can use some ice damage to deal more damage and not have risk to miss.
You need to be really fast, because they disappear right after they walk into water.