Ghostcrawler is strictly a tamable hunter pet. He is currently unkillable due to a couple of abilities that he has. First of all he continuously disappears while patrolling and while engaged in combat. This is not a stealth, he actually disappears. (You can see this in the video I have below. I was tracking stealth and beasts at the time, and when he disappeared I couldn't see him on my mini map any more.) When Hunter's mark is put on Ghostcrawler it will not remain on him when he disappears as well. The other reason he cannot be killed is his Nerfbat ability. It hits extremely hard, stacks and hits everybody within range.
Taming: You NEED to be level 85 to tame Ghostcrawler because he is a level 85 mob. He also hits VERY hard while taming, and freeze/frost traps do not work on him so the extra hit points and deterrence will help you. He can be tracked with the track beast feature, but will not show on your mini map when he disappears. When he disappears he cannot be tracked with track hidden.
For taming in the video below, all I did was hit deterrence right before I started taming to mitigate some of his damage. As you can see he still got me down to about 45% health when it completed.
Ghostcrawler is also a spirit beast, he can only be tamed by hunters that have the top-tier talent from the Beast Mastery tree Beast Mastery which allows the taming of exotic pets.
Ghostcrawler is not affected by phasing, if you have only done a few quests in the zone or completed all of them you will still be able to see him if he's up.
I'd also like to note that there is a very large incredibly unfriendly elite mob named Kolorath that patrols the area where Ghostcrawler patrols. He pretty much one-shots people, so be very careful where you afk camp, and if you see him...run.
He is also one of eight rare spawns in Vashj'ir. All of them are:
- Ghostcrawler (Spirit Beast Crab) - For lvl 85 BM hunters, can not be killed
- Mobus <The Crushing Tide> - Group Boss, drops a nice epic polearm
- Poseidus (Sea Horse) - Drops Reins of Poseidus, a bind on use underwater mount
- Shok'sharak - Faceless one, drops some booties
- Lady La-La - Drops a nice level 80 healer trinket