like DUCKY said, it spawns randomly. I do know for a fact, from asking admins, that you do not get creds for hitting the Giant Blob with bombs/arrows. It can only be the sword. I am pretty sure you do not need to hit the Blob a lot to get spoils, but there are rumors that the more you hit it the better prize you will get from the spoils.
Who would like some pie?
I'm a professional goose, trust me.