pawsplay said:
I have a hard time seeing a dragon's bite and a horse's bite as "one natural weapon."
There are stories that say that Odin likes to wander among mortal men in various disguises - a peasant, a bird, a cat - but that an observant man can always recognise him, because one eye is missing in every form he takes.
I can imagine, for example, a magical gold tooth, that becomes a part of a person (so that it is not considered an item)... and that the bearer of such a tooth might be known in any form he took (as long as it's a form with teeth), by his one gold fang.
And I would have no problem accepting that while the form might change, the concept of 'this is my mouth' is reasonably constant. We do not take the druid, smoosh him into a formless blob of dough, and start constructing a horse from scratch; we shape the druid's ears into horse's ears, the druid's legs into horse's legs, and the druid's teeth into horse's teeth. We shape the druid's ears into dragon's ears, the druid's legs into dragon's legs, and the druid's teeth into dragon's teeth.
And so what the horse bites with, and what the dragon bites with, are at their essence the same conceptual entity - the druid's 'bite'.
I can see how it could be argued that one GMF cast on the druid's 'bite' - whichever form he happened to be in at the time - would apply to the druid's 'bite' in any form he occupied for the duration of the spell.
-Hyp.