WoWDB

As already mentioned, a rabbit is a great choice against the spirit. I personally use my cricket for this fight.
The passive critter ability breaks you out of stuns, but using cocoon right off the bat will block the next attack which (in my experience) is always Rupture, its hardest hitting move.

If you're having trouble killing this guy, use a Tolai Hare. The critter passive will get you out of his stuns, while burrow and evasion just make the fight pretty much trivial.