Hi, I am a level 50 grandmaster and haven't played in years. Last time I played grizzleheim was just introduced and I really never bothered with it. Can anyone guide me where to go or what to do now?
While the link to the KI blog might help a bit, your best bet is to visit Wizard Central. There you can check out all the new spells for whatever school you are, and the quest trees for most of the worlds. Not sure where you left off, but there's a LOT to catch up on. (And there are spells for each school that require Grizzleheim and it's connected world, Wintertusk. You're going to have to do that to get those spells, and an additional school pet.)
Below is a link to the quest trees. You'll have to sort our your school on your own since you don't indicate which one it is:
Grizzleheim itself can be long and tedious, especially considering the XP rewards are low. But once you complete it, you can get into Wintertusk which has phenomenal XP.
I'm guessing at level 50, you had completed Dragonspyre before you left. Depending on what's important to you, you can do Celestia first, or you can get into Grizzleheim and Wintertusk and come into Celestia a little stronger.
There are some cool astral spells in Celestia that will help you with your battles. It'll probably take some time to get back into the swing of things. If you enjoyed it up until Dragonspyre, you'll probably be pretty happy with what lies ahead.