What is the name of an old MMORPG where you could morph into the monster you killed if it dropped a sphere?

I played the game maybe 5-7 years ago and I remember it having flying quests with booster packs (I think). There was also a section of the map with caves where there were flying creatures that shrieked. There were a bunch of different monsters, including some that were really tall with two legs and could run fast as hell. The beginning monster looked like a worm and made this weird noise and rolled. I think the category was Science Fiction/Fantasy but I cannot for the life of me remember the game name.