DANGEROUS! Due to the large drops it has and the high possibility to get rich very quickly, without getting hit by the Spirit Beast, not only is he aggressive, but it will deal a maximum of around 50 HP. Using Protect from combat will cause it to deal about half of the maximum HP.
A little warning, using prayer it managed to kill me rarther quick, unless you don't mind the high possibility of losing all of your items, I would not solo! You stand much better chances in numbers of 2 or 3. The more you have the safer it will be.
This is our hardest boss as of now!
I have run some other updates after the above, so I will add now what I have done.
The Spirit Beast being aggressive would attack you upon entrance to the area, so this would make killing Dagganouths impossible! So I have moved the Spirit Beast to it's new home. This happens to be right outside our little church, well, slightly further out, I hope for our lives, it is far away enough for us to survive...
You can get there to slay the beast by typing the command: ::spirit
Final note: It has more rewarding drops...