You have to be lvl 40+, and get the quest Blood Brothers, which is the quest to beat Jotun and his 3 brothers. 3 of the grendels are 4,000 health and the 4th is around 1,200. You WILL need help preferably 3 people minimum.
You will finish Grizz when you get the quest to go to the Fortress in the Glacial Waste. There are a few smaller quests you have to do there in order to get into the Fortress. That is where the Bloodbrothers are and I would suggest having a couple of friends at least to help with that battle.
You have to be lvl 40+, and get the quest Blood Brothers, which is the quest to beat Jotun and his 3 brothers. 3 of the grendels are 4,000 health and the 4th is around 1,200. You WILL need help preferably 3 people minimum.
John Smith lvl54 Life
You need to beat Jotun in order to get to Ravenscar. Not Wintertusk.