The Dis's page

The Dis wrote:

So what is an effect? Is it defined anywhere within the rules?

Anything that varies based on creature type.

There's no difference between an animal and a magical beast when it comes to "at what negative HP value does it die?"

So does the companion gain darkvision for example?

So what is an effect? Is it defined anywhere within the rules?

Simple one, how many negative hitpoints before a familiar dies?
The rules appear to specifically call out that they're a normal animal which would be -10hp. However another player insists that like a character it's to -con because they count as a magical beast for 'effects'.
What an effect is is not defined anywhere that I can see.

Don't get me wrong, i'm not disagreeing with anything any of you are saying, infact i agree with it all. I just think that the rules on this are very contradictory.

Both your arguements there are what i'd expected to hear. But to me what page 91 says is that arcane casting only requires one hand to do (I agree that yes, this hand should be able to move freely). Therefore why is there a problem with having armour or a shield on the other unused arm?

On page 91 (below the climbing DC check table) of the core rulebook it states that when climbing arcane spells can be cast, the caster simply clings on with only one hand. It makes no mention of any penalty for this. So to confirm this is one hand that can make no somatic contribution to the casting of a spell and yet has no penalty.
Why then do shields/bucklers and using the optional rules for armour parts of armour on only one arm incur an arcane spell failure chance? The hand under these circumstances is still available for some contribution.
Seems utterly backwards to me.

An issue came up in a recent adventure session whereby I as a ranger managed to hit an ancient red shadow dragon with a greater arrow of dragon slaying only to be told that it was immune to any effects the arrow might have had...Needless to say we as a group had a nice long discussion about it and I accepted the GMs arguement that tough, I did no damage as the arrow needed to be attuned to undead slaying. (I killed the wyrm in the next round anyway).

Does this seem correct as I still find it strange that a dragon is immune to arrows of dragon slaying.