Let's say a magician throws possession in a bugbear. Now, this bugbear has spent some time in questionable places and has contracted both Filth Fever and Mindfire, the first is a disease that causes Dex and Con damage, the latter is a disease that causes Int.
The wizard still owns the bugbear when the diseases have their next skill damage tick. Who receives the damage of the skill: the bugbear or the magician?
The second paragraph of the possession the description of the spell is read as follows (emphasis mine):
If you succeed, your life force occupies the host's body. The soul of the host is imprisoned with you, but you can still use your own senses (although you can not exert any influence or use purely mental abilities). You can communicate telepathically with the host as if you shared a common language, but only with your consent. You maintain your intelligence, wisdom, charisma, level, class, base attack bonus, base salvation bonuses, alignment, and mental abilities. The body retains its strength, dexterity, constitution, hit points, natural abilities and automatic abilities.. A body with additional limbs does not allow you to perform more attacks (or more advantageous attacks with two weapons) than normal. You can not activate the extraordinary or supernatural abilities of the body, nor can you cast any of its spells or similar abilities.
Because of this, I assume that only the body (the bugbear) would get the Dex and Con damage from Filth Fever, although I can not find any decision about it. But what about the Mindfire Int damage?
Who gets the damage int? The magician, the bugbear or maybe both?
It seems to me a difficult question because there two minds in the same body, unlike similar possession spells like magic jug that eliminates the original soul of the body.
On a related note (and if this should be a separate question, I apologize):
How would you like spells Weak mind Work by targeting a body inhabited by more than one mind?